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Pass T A ^ J_^ 
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DEPARTMENT OF COMMERCE 



Technologic Papers 



OF THE 



Bureau of Standards 

S. W. STRATTON. DIRECTOR 



No. 82 

FAILURE OF BRASS. 1.— MICROSTRUCTURE 

AND INITIAL STRESSES IN WROUGHT 

BRASSES OF THE TYPE 60 PER CENT 

COPPER AND 40 PER CENT ZINC 

BY 

PAUL D. MERICA, Associate Physicist 

and ' - 

R. W. W60DWARD> Lalx)ratory Assistant 
Bureau of Standards 



ISSUED JANUARY 29, 1917 




WASHINGTON 

GOVERNMENT PRINTING OFFICE, 

1917 



Bureau of Standards Technologic Paper No. 82 



•1 



fl fi 



Specimen No. S 

Fig. I. — Season cracked brass rod 



Specimen No. ifii 



DEPARTMENT OF COMMERCE 



Technologic Papers 



OP THE 



Bureau of Standards 

S. W. STRATTON. DIRECTOR 



No. 82 

FAILURE OF BRASS. 1.— MICROSTRUCTURE 

AND INITIAL STRESSES IN WROUGHT 

BRASSES OF THE TYPE 60 PER CENT 

COPPER AND 40 PER CENT ZINC 



BY 



PAUL D. MERICA, Associate Physicist 

and 

R. W. WOODWARD, Laboratory Assistant 

Bureau of Standards 



ISSUED JANUARY 29, 1917 




WASHINGTON 
GOVERNMENT PRINTING OF 
1917 



OrLuT^ 









'^ 



ADDITIONAL COPIES 

OF TmS PUBLICATION MAY BE PROCURED FROM 

THE SUTERINTENDENT OF DOCUMENTS 

GOVERNMENT PRINTING OFFICE 

WASHINGTON, D. C. 

■ AT 

25 CENTS PEK COPY 



A complete list of the Bureau's publications may 
be obtained free of cbaige on application to 
the Bureau of Standards, Washington, D. C. 



D. of D. 
FEB 23 1917 



^ 
^ 



\ 



FAILURE OF BRASS. 1 .— MICROSTRUCTURE AND 
INITIAL STRESSES IN WROUGHT BRASSES OF THE 
TYPE 60 PER CENT COPPER AND 40 PER CENT 
ZINC 



By Paul D. Merica and R. W. Woodward 



CONTENTS 

Page 

I. Introduction 3 

1. Some experiences with brass failures 4 

2. Literature on season cracking 12 

II. Investigation op brass materials 17 

1. Ihtemal, initial stresses 29 

(a) Measiurement and calculation 30 

(b) Values of initial stresses 32 

(c) Radially nonsymmetrical stresses 36 

(d) Rapid methods for initial-stress determinations 37 

(e) Removal of initial stresses by annealing 39 

2. Structure of brasses and its relation to failures 42 

3. Some corrosion and acceleration tests 48 

4. Hardness values 50 

5. Discussion of results 51 

III. Conclusion 61 

Appendix. — Specifications for wrought brass 63 

List of photographs and photomicrographs 7i 

List of initial stress diagrams ' 72 

1. INTRODUCTION 

"Can a brass or bronze of high tensile strength be reUably pro- 
duced which can be used safely for important permanent structures 
in such parts as bolts and other rolled, drawn, extruded, or forged 
shapes?" Thus has a well-known engineer recently expressed 
what may be regarded as the fundamental question which has 
arisen, as a consequence of the modern tendency among engineers 
and constructors to substitute such materials for steel, because of 
their superior resistance to corrosion, and of the recent failure of 
large amounts of brass used for structural purposes. It is evident 
that the greater incorrodibility of these copper alloys is of no prac- 
tical value if the alloys are not at the same time mechanically 
stable and with well-defined behavior toward service loads and 
stresses, such that from physical tests their reliability in service 

may be definitely predicted. 

3 



4 Technologic Papers of the Bureau of Standards 

The recent experience of a number of users of brass for struc- 
tural purposes has indicated that, in this sense at least, brass is not 
as reliable as steel; the results of the ordinary physical tests of 
brass are not always sufficient to enable the engineer to form a 
definite opinion concerning the serviceability of the material. 
Properties and characteristics other than those determined in the 
tensile and hardness tests must be considered in using brass for 
structural purposes; the relation of certain of these to the occur- 
rence of failures of these materials has been studied in the course 
of tests and investigation of the last two years. 

1. SOME EXPERIENCES WITH BRASS FAILURES 

This work was taken up in connection with tests, made for the 
New York Board of Water Supply, of failed brass bolts, which had 
been in service in the construction of the new Catskill Aqueduct, 
which is to supply water to the city from the watersheds of the 
Catskill Mountains. 

In view of the fact that most of the equipment and materials 
used in this construction would be subjected to the corroding action 
of both water and the atmosphere, a substitute was sought for 
steel, which would ordinarily be used, and it was considered possi- 
ble to find a brass which would have mechanical properties com- 
parable with those of steel and yet be practically incorrodible. As 
such a substitute so-called manganese "bronze" was chosen and 
also other similar brasses, which all have approximately the same 
composition, namely. 

Per cent 

Copper 58. o to 62. o 

Zinc 36. o to 40. o 

Tin 5 to I. 5 

Iron oto I. o 

Manganese ; oto .2 

These materials, as wrought, have ultimate tensile strengths 
ranging from 50 000 to 75 000 pounds per square inch and seem 
admirably adapted for this purpose, so much so that some 3 000 000 
poimds of these materials, in the form of castings, wrought rods, 
and tubing, have been installed on the aqueduct. Serious diffi- 
culties have, however, been encountered in their use and many 
failures have occurred, some under moderate or large service 
loads and some, on the other hand, merely during shipment and 
storage. "Large ^ numbers of brass bolts have been foimd cracked 

' A fuller account of the experience of the New York Board of Water Supply with these brasses will be 
found in a paper read in 1914 by A. D. Flinn before the municipal engineers of New York City, entitled 
■'Brass in Engineering Construction," and from which quotation is made here and more fully on page 5. 



Failure of Brass 5 

and broken in their packing cases after storage through a winter, 
but having never been stressed ; others never exposed to low tem- 
peratures and never stressed have been found in similar condi- 
tion. These bolts ranged from one-half to 2}{ inches in diameter. 
Similarly, flat bars, rolled plates, and long rods supporting only 
their own weight have been found cracked or severed after a lapse 
of a few or many months. Flanged one-fourth-inch plates 
riveted together, after careful inspection being in apparently 
good condition, were found some months later to have incipient 
and well-developed cracks, with many rivets cracked or yielding 
to relatively light blows from a hand hammer. Many upset bolt- 
heads have come off. Hundreds of bolts have broken under 
tension after short or long intervals. No brand or make of brass 
or bronze has wholly escaped. Manganese bronze, naval brass 
(including a well-known bronze and its imitation), and Mimtz 
metal, from all the manufacturers who have furnished any con- 
siderable quantity, all have failed. Hitherto castings and large 
forgings have been exempt, or at least failures in them have not 
been discovered except in a few cast bolts and nuts" (and it 
should be added in the case of bumed-in castings at or near the 
burned-in areas) . 

The New York Board of Water Supply is not alone in its expe- 
rience with brass failures, although the amounts of material 
involved in its case lend it prominence. The engineer's depart- 
ment of the city of Minneapolis have lately — 1914 — experienced 
similar difficulties with naval brass strainer plates and bolts 
installed in their new filter plant, and some interesting instances 
of failures of this type occurring in manganese-bronze bolts used 
in the construction work of the Panama Canal have come to our 
attention. 

Specimens from these three parties form a large part of the 
material investigated, and for this reason a more detailed account 
of the difficulties encountered with these materials by the New 
York Board of Water Supply, the engineer's department of the 
city of Minneapolis, and the engineers of the Panama Canal is 
given below in the form of quotation from published article or 
correspondence . 

QUOTATION FROM MR. FLINN'S PAPER (LOG. CIT.) CONCERNING BRASS FAILURES ON 

CATSKILL AQUEDUCT 

Claims of the brass or bronze makers, backed up by tests and experience, led the 
engineers of the Catskill Aqueduct, after careful investigation, to adopt some of these 
copper-zinc alloys for extensive use where their noncorrodibility and other good 
qualities claimed for them made them especially suitable. It is safe to say that on 



6 Technologic Papers of the Bureau of Standards 

no other single engineering enterprise have such large quantities been used, the total 
being nearly 3 000 000 pounds. Of castings, ranging from a fraction of a pound to 
22 000 pounds each, there have been a total in excess of 2 000 000 pounds; of forgings, 
a large proportion of the remainder, varying from small bolts to sluice-gate stems 
about 6 inches in diameter, 31 feet long, weighing 3 200 pounds apiece. Plates, rods, 
and shapes make up the balance. Manganese bronze constitutes a very large propor- 
tion of the total; "naval brass," including Tobin bronze, was used in large amounts; 
various common brasses and special compositions make up the relatively small remain- 
ing quantity. * .* * 

It is not with these large brass castings, which are so important, nor with the large 
forged stems of slujce gates and valves, nor with the smaller castings, excepting a 
few cast bolts, that the interesting and trying subsequent experiences have been 
had. Designing, casting, forging, machining, testing, and installing these large 
objects have involved the solving of many interesting problems, but the unexpected 
metallurgical developments have occurred in the smaller objects, such as bolts, lad- 
ders, and pipes, which when they go wrong have capacities for trouble quite dispro- 
portionate to their sizes. 

These numerous and various brass articles have been made by a number of manu- 
facttuers scattered through New England, New York, Pennsylvania, and New Jersey. 
Their methods and equipment were of their own selection with very few exceptions, 
and apparently were developed by experience. Some of these manufacturers of brass 
or bronze have had experience equaling or exceeding, in number of years, the period 
of manufactiire of modem steels. Consequently the troubles which have occurred 
so extensively on the Catskill Aqueduct have been all the more astonishing, and lack 
of information concerning such troubles the more incredible. Not alone the Board of 
Water Supply, but other users have also had trouble of one kind or another, but knowl- 
edge of such trouble has come to hand only within relatively recent time. Just when, 
as to date or in the state of development of brass manufacture, these troubles began 
or how extensive they have been has not yet been learned. Possibly they might 
still be considered occasional or accidental, but for the large and concentrated use 
of these alloys on the Catskill Aqueduct under such supervision as led to the detec- 
tion of the difficulties and a thorough investigation of their causes, together with their 
bearing upon the use of such alloys in engineering construction. * * * 

No suspicions of definite troubles were developed until the fall of 1913, when 
numerous bolts and rods were found cracked. The number and character of the 
failures detected strongly suggested that they were more than accidental or sporadic. 

Failtues were the more distvirbing because the specifications had been drawn care- 
fully, in the light of information then in hand, and practically all the metal accepted 
had been subjected to careful inspection, including the standard physical tests and 
chemical analyses. Much of the metal accepted had shown physical qualities in 
generous excess of the specified requirements. It is quite tmthinkable that the 
manufacturers were not honestly endeavoring to fulfill the specifications and furnish 
satisfactory materials, although they may have been misguided as to means and 
methods in some instances and somewhat influenced by commercial considerations. 
What, then, was the root of the matter? It is the answer to this question which is 
still sought. * * * 

The results of a number' of representative inspection tests are given, as 
examples, * * * 



I 



Failure of Brass 

Typical results of physical tests of brasses used on the Catskill Aqueduct 



Yield, pounds per square inch 



Ultimate 

strength, 

pounds 

per square 

inch 



Elongation, 
per cent 



Reduction, 
per cent 



Fracture 



Forgings: 
36 500 
37SOO 
38250 
52 500 

49300 

50 000 

43 S°° 
36000 



73 ISO 

75 75° 

76 900 

77 100 
76 150 
75 35° 
70 000 
67 soo 



41- S 
35-5 
35-5 
31- o 
33-5 
31.0 
34- o 
40- 5 



46.8 
43-9 

46.8 



47.0 
43-5 



Irregular. 

Do. 

Do. 
Irregular, silky. 
Silky cup. 
Irregular, silky. 
Irregular. 

Do. 



But little trouble has been experienced with the pipes furnished by reputable 
manufacturers in recent years. A few small pieces have failed on the Catskill Aque- ' 
duct. There is but small excuse for supplying other than dependable brass pipe 
nowadays, as correct methods of manufacture are well known in the trade. 

Defects in large plates, in bolts, rods, side bars, and rungs of ladders and in similar 
objects constituted the most important lots of failures on the aqueduct. Many of 
these articles had not yet been installed, but had been in storage in some instances for 
many months. These defective pieces all had cracks, usually circumferential, part 
way or all the way around. Some cracks were very fine and only superficial; others 
gaped open and penetrated the metal deeply. In some cases the whole or nearly the 
whole cross section was affected in bolts from one-half to 2^ inches in diameter; some 
were found severed and others broke with a light blow or pull. Specimens which on 
first examinatian seemed free from this cracking developed it later; two or three 
years have passed in some cases before the defects developed so as to be detected. 
Investigation disclosed the fact that similar defects had been observed by others in a 
variety of metals, but chiefly in drawn or otherwise cold-worked brasses. Although 
not then satisfactorily explained, this trouble was known among brass men as "season 
cracking." * * * 

After the discovery of the extensive season cracking and a partial investigation of 
its causes, it was decided to use plain extruded or hot-rolled rods wherever practicable 
and to anneal all material which had to be drawn or rolled cold. It was hoped that 
by these methods of manufacture further trouble of this kind would be avoided, but 
unfortunately this has not proved to be the case. Plain extruded, hot-forged, and 
annealed brass rods, supposedly free from initial stress, have also failed in disturbingly 
large quantities. * * * 

Designers have been misled to some degree by the representations of the manufac- 
turers that certain bronzes (brasses) possessed great strength and other excellent 
qualities, and in some cases would perform practically the same duty as steel or a little 
more. Seemingly both maker and user have misinterpreted the results of the usual 
standard laboratory tests from lack of knowledge of characteristics of the copper alloys 
not revealed by such tests. Experience on the Catskill Aqueduct indicates that the 
bronzes (brasses) as supplied under contract, with careful inspection following the 
established methods, would not perform the expected duty. Indeed, as these inves- 
tigations have proceeded it has become evident that the engineer's present necessity 
is not merely an explanation of certain failures of brass, but a fundamental knowledge 
of the physical characters and capacities of this group of alloys — ^knowledge which will 
be a safe and dependable guide in their manufacture, inspection, and use. 



8 Technologic Papers of the Bureau of Standards 

To summarize the Catskill Aqueduct experiences: Large numbers of brass bolts 
have been found cracked and broken in their packing cases after storage through a 
winter, but having never been stressed; others never exposed to low temperatures 
and never stressed have been found in similar condition. These bolts ranged from 
one-half inch to 2^ inches in diameter. Similarly flat bars, rolled plates, and long 
rods supporting only their own weight have been found cracked or severed after a 
lapse of a few or many months. Flanged one-quarter-inch plates riveted together, 
after careful inspection being in apparently good condition, were found some months 
later to have incipient and well-developed cracks, with many rivets cracked or yield- 
ing to relatively light blows from a hand hammer. Many upset boltheads have 
come off. Hundreds of bolts have broken under tension after short or long intervals. 
The failures have been so numerous and important as to have caused the gravest 
apprehension and led to the substituting of steel for brass in many cases in spite of the 
recognized disadvantage of steel as to corrosion which the engineers had sought ear- 
nestly to avoid. No brand or make of brass or bronze has wholly escaped. Manganese 
bronze, naval brass (including a well-known bronze and its imitation), and Muntz 
metal, from all the manufacturers who have furnished any considerable quantity, all 
have failed. Hitherto castings and large forgings have been exempt, or at least fail- 
ures in them have not been discovered, except in a few cast bolts and nuts. 

For the designing and constructing civil and mechanical engineers, the following 
questions should be satisfactorily answered if they are to continue the use of these 
brasses or bronzes for important purposes: 

Can a brass of bronze of high tensile strength be reliably produced which can be 
used safely for important permanent structures in such parts as bolts and other rolled, 
drawn, extruded, or forged shapes? 

What should be the specifications for such brasses or bronzes? 

What inspection methods and tests should be used? 

By what tests can the tendency to subsequent failure be detected at any time after 
manufacture? 

What working stresses may be used safely for these various alloys? 

Will these brasses or bronzes deteriorate by reason of constantly applied or frequently 
repeated stress; i. e., will they fail from fatigue? 

QUOTATION FROM LETTER REPORT BY THE CITY ENGINEER OF THE CITY OF MINNE- 
APOLIS CONCERNING DIFFICULTIES WITH BRASS STRAINER PLATES AND BOLTS 

Early in the spring of 1912 the city of Minneapolis advertised for bids on the entire 
strainer system for their new filter plant then under construction . Among the various 
items comprising the strainer . system were 1224 middle strainer plates, 2448 side 
strainer plates, 3672 one-fourth-inch brass bolts, 12 240 one-fourth -inch brass U-bolts 
and 12 240 one-half-inch anchor rods, all as per drawings herein shown and according 
to the specifications noted below. [See Appendix.] * * * 

During the fall and winter of 1912 the entire lot of plates and bolts were placed in 
their respective places in the various filter boxes and early in January, 1913, 6 of the 
12 filter units were placed in operation. 

No trouble whatsoever was experienced for the first 3 o or 40 days of operation . After 
the above period, however, the center plates began to break longitudinally through 
the center, and soon after a number of the side plates cracked crosswise at the end 
nearest the center of the filter box. At first no great attention was paid to the break- 
age, but before the summer was very far advanced the breaking of plates was an 
everyday occurrence and became so very bad that it was necessary to remove the 
entire lot from each filter box (one at a time) and replace the broken plates with new 
hard brass plates and reinforce all the remaining center Tobin bronze plates with a 
strip of one-eighth-inch sheet brass riveted longitudinally along the center of the 
plate. This reinforcement improved matters somewhat but did not obviate the 
breakage entirely . 



Failure of Brass 9 

Tensile and bending tests were made on pieces of metal cut from the broken plates, 
with results that were very satisfactory. * * * 

A peculiar thing about the whole affair was that very few of the side plates broke, 
and when they did break the fracture was at right angles to that of the center plates. 
After a careful study of the matter, it was decided that the design, as used, had many 
faults, and that by redesigning the plates and their connections, making the plates 
heavier, decreasing the friction through the openings and reinforcing by ribs against 
the greatest pressure, all breakage would be overcome. * * * 

A design for improving the filter strainer system as per accompanying plans was 
immediately prepared with the specifications noted below [see Appendix] to govern, 
all unit stresses being the minimum stress as set forth in the pamphlet hereinbefore 
mentioned. * * * 

Immediately upon the arrival of the material for the new strainer system one filter 
box was equipped coriipletely and the wash water turned on for a test before any gravel 
or sand was placed in the filter box. Unusual agitation of the water was noticed at a 
number of places, which upon investigation proved to be caused by the breaking of a 
number of the anchor bolts, as shown by samples in the city engineer's ofiBce. These 
broken bolts were removed and replaced by new ones, again tested, found all right, 
and the gravel and sand added immediately. After operating the filter for about a 
week, the filter again showed breaks. The sand and gravel were removed and the 
entire lot of center plates with their anchor bolts taken out. There was scarcely a 
plate that did not have one or more broken or cracked anchor bolts, and in some cases 
the plates themselves were cracked. Believing that the above breakage of bolts was 
due to flaws in the material and that the plates broke on account of too great a pressure 
concentrated at one point due to the breaking of the bolts, it was decided to replace the 
bolts by new ones, but before doing so, to test all bolts in tension to a dead load of 
800 pounds each, also to test a number of bolts to failure for both tension and cross 
bending. Accordingly a number of bolts were tested on a testing machine until the 
hook at the end straightened out, which took place at a load varying from 1420 pounds 
to 1350 pounds each. In the bending tests all bolts were bent through an angle of 
180° flat on themselves without showing fracture on the bent portion. When tested 
to failiu-e in direct tension, the bolts gave a unit tensile stress varying from 71 000 
pounds to 100 000 pounds per square inch. Therefore, it was concluded that the 
material was probably all right and safe to use after being tested to the 800-pound load. 
Before placing any tested bolts in the filters, each bolt was examined carefully, some 
by means of a low-power microscope. No flaws being evident, the bolts and plates 
were again put in place. Before testing the strainer system, the bolts were gone over 
carefully and about 10 per cent found to be loose, caused by the cracking or complete 
failure of the bolt as before noted. All bolts and plates were again removed and a new 
lot of bolts heated in a fiunace to a cherry red, then quenched in lukewarm water, 
tested to 600 pounds (all that they would stand without straightening out), and put 
in place. This improved matters a great deal, no failure was noticed in the filter so 
equipped until about four weeks after it was placed in operation, when a number of 
the strainer plates were blown completely from their seats and up through the gravel, 
which proved upon investigation due to the breakage of the anchor bolts as before 
noted. At this time some of the strainer plates again began to fail, and one plate was 
found cracked longitudinally through the center before it had even been placed in 
the filter. 

The plates instead of cracking as in the original installation (longitudinally through 
the center) seemed to crack in every manner possible and followed no definite lines, 
appearing very similar to the checks in sun-dried lumber. Samples of the broken 
bolts and plates were sent to the testing laboratory, the contractor, and the manu- 
facturer, but no one seems to be able to explain the cause. 



lO 



Technologic Papers of the Bureau of Standards 



A test, by means of a presstire gage, was made of the maximum water pressure under- 
neath the plates and found to be ■]% pounds per square inch, amounting to a pull of 
only 270 pounds on each hook bolt, which was far below the original stress of from 600 
to 800 pounds to which the bolts were tested before installation. 

QUOTATION FROM LETTER REPORT BY THE CHIEF QUARTERMASTER, PANAMA 
CANAL, CONCERNING THE FAILURE OF MANGANESE-BRONZE BOLTS 

About the middle of October last year the operator of the Gatun Hydroelectric 
Station advised that one of the counterweights of spillway machine No. 13 had dropped 
into the pit without warning and at a time when the machine had not been operated 
for some time, the gate being in the closed position at the time of the accident. * * * 
Under date of December 17, 1915, the electrical engineer was requested to make a 
report of his investigations in connection with the breakdown, and a copy of his reply 
dated December 21, 1915, is attached [immediately following]. 

I have to report that all four bolts on the west counterweight of Gate 13 at Gatun 
Spillway broke under the head while the counterweight was at rest with the gate 
closed. The fracture indicates that the metal (manganese bronze) was burned 
when the heads were upset, as all four bolts failed within an inch of the head. 

Test pieces were cut as near the fracture as possible and tested in the Riehle 
testing machine at Balboa shops, with the following results: 



Sample 



Diameter 



Area 

in 
square 
inches 



Elastic 
limit 
per 
square 
inch in 
pounds 



Ultimate 

stress 

per 

square 

inch in 

pounds 



Elonga- 
tion, per 
cent in 
2 inches 



Reduc- 
tion of 
area, 
per cent 



No. I 
No. 2 
No. 3 
No. 4 



H inch. 
I/3 inch. 
Kinch. 
M inch. 



o. 196 
. Z96 
. 196 
. 196 



49 650 



47 750 



73 75° 

74 800 
72 45° 
74650 



26. o 
28.0 

31-5 
28.0 



39-8 
42.9 

43-4 
42.4 



The physical test requirements of the specifications in Circular No. 661, under 
which these bolts were purchased, are as follows: 

Ultimate stress per square inch in poimds 70 000 

Elastic limit per square inch in pounds 40 000 

Elongation, per cent 25 

Reduction of area, per cent 25 

An examination of these bolts shows plainly, aside from the fracture, that the 
metal had been burned, as stated, and in order to ascertain whether or not similar 
results were to be expected in other bolts in the remaining counterweights we 
removed two bolts from the adjacent counterweight on this gate. These bolts 
indicated no overheating or btUTiing, and tests were made to determine the physi- 
cal strength of the bolts under the head. They were tested in the same machine 
as the samples above referred to and were subjected to a tension of 100 000 pounds, 
with no signs of failtire. The bolts were then turned down to a diameter of 1.125 
inches and test again made, with the following results: 



Sample 


Ultimate 

stress 

per 

square 

inch in 

pounds 


Area 

in 
square 
inches 


Remarks 


No. I 


61 400 
63900 


0.994 
•994 


Head of bolt pulled off. 


No. a 


Do. 







Failure of Brass 1 1 

This result indicates a rather low ultimate stress for first-class manganese 
bronze, which should be around 95 000 to 100 000 pounds per square inch, but 
the fracture indicates good metal. 

Each spillway counterweight consists of 56 cast-iron blocks weighing 750 

pounds each and a base plate weighing 3700 pounds, making the total weight 

45 700 pounds. This weight is supported from the counterweight yoke with 

four manganese bronze bolts, each i)4 inches in diameter. Assuming that the 

load is equally distributed between the four bolts, there is then a load of 11 425 

pounds. The bolts being ij^ inches in diameter have an area of 2.405 square 

inches, which gives a load of 4750 pounds per square inch, and from the results 

of the second test gives a factor of safety of approximately 15. 

About the middle of November, 1915, and shortly after the accident to the Gatun 

Spillway counterweight bolts, the superintendent of the Gatun Locks advised that 

one of the counterweights of the guard-valve machines at that point had dropped 

into its pit without any resulting damage to any of the equipment, however. * * * 

The superintendent of the Pacific Locks has reported, tmder date of December 30, 

1915, as follows: 

I have to advise that this morning a second broken bolt was found in the spill- 
way counterweights. The pieces have not yet been recovered for examination, 
but the location of the break is similar to that found yesterday. 

The heads of the^e bolts were inspected as far as possible visually about two 
months ago. I also had visual inspection of the rest of the bolts made this morn- 
ing, and as far as could be seen the rest of the bolts were still intact. * * * 

The head from the bolt found broken yesterday is being forwarded to you 
under separate cover. You will note that the fracture is quite crystalline, and 
that there was practically no reduction in area. There appears to have been 
practically no elongation. The dark stain in the fracture I believe comes from 
the iron, and it would indicate that the metal apparently cracked progressively 
until the area became so reduced that finally rupture occurred. * * * 

One or two small surface cracks are visible with the aid of a small magnifying 
glass in the body of this bolt. * * * • 

The superintendent of the Atlantic Locks reported as follows: 

1. With reference to your letter of December 17, 1915, I have to report that on 
October 21 the U bolt supporting the counterweight on guard valve No. 226 
failed, dropping the counterweight into its well. 

2. The U bolt which is forwarded separately for test, if desired, was broken in 
two places, namely, at top of one of the nuts and at tjie shoulder of the U oppo- 
site to first break. 

3. As the roller trains were connected through separate chains to the main 
counterweight, the J^-inch connecting shackles failed when the counterweight 
dropped. No other parts were damaged. 

4. The guard valves were not in operation when failure occurred, the last 
operation being two days previous to the accident, when they were given rather 
heavy service in an attempt to cut down the leakage through them. 

5. The total weight of the counterweight is 28 580 pounds, which under normal 
condition would make the load on each leg of the U bolt 14 290 pounds. Indi- 
cations are that the weight was not equally divided, as the legs now differ in length 
by approximately i inch, and it is not believed the distortion produced by the 
accident could have amounted to so much. Assuming all the weight to have 
been on one leg the total stress would have been 28 880, or 17 610 pounds per 
square inch for the area at the shoulder break of 1.623 square inches. The I. C. C. 
specifications given in Cir. 636 for rolled bronze require an ultimate strength of 
65 000 pounds per square inch and elastic limit of one-half this. 



1 2 Technologic Papers of the Bureau of Standards 

6. The fracture at the nut shows a crystalline structure with an indicated 
fibrous structure at right angles to the length of the bolt. 

7. The fracture at the shoulder shows about one-third fibrous and two-thirds 
crystalline structure. A vertical crack i inch long, showing on one side of the 
bolt, marks the plane between the two areas. 

8. The remaining U bolts have beeJi examined and indications are that they 
are o. k. I recommend no further action be taken. 

Although, as will be brought out later, some differentiation 
in characteristics can be made between these various instances of 
brass failures, they bear a striking similarity to that type of failure 
known as "season cracking," connoting the formation of cracks 
or fissures in wrought-brass articles some time after their manu- 
facture, although the articles had been sound originally and had 
even passed rigid inspection and test. Examination of such 
material, in the usual way, will show it to possess desirable physi- 
cal properties, as indicated by the tensile test, satisfactory chemical 
analysis, and sound structure, as shown by etching tests and the 
microscope. Apparently no usual cause can be assigned for the 
defective nature of this material; these failures will often occur 
before the application of any appreciable external stress or load. 
This type of failure is perhaps most common in tubes, but is found 
also in all types of wrought brass, be they rolled, drawn, stamped, 
or spun; its seriousness arises from the fact that ordinary tests 
will not indicate the possibility 01 its occurrence. 

The manufacturer knows this phenomenon most familiarly as 
"fire cracking," or the cracking of the drawn or cold-worked 
material upon putting it in the annealing furnace; samples of 
such "fire-cracked" material are generally not difficult to find in 
a brass mill. 

2. LITERATURE ON "SEASON CRACKING" 

The first reference to failm-es of the type of season cracking is 
given by Diegel,^ who describes instances of such failures in brasses 
and bronzes, and ascribes it to the presence of initial stresses 
caused by cold working and to the gradual "after flow" of metal,- 
which he claims continues even after the cold working of the 
metal has ceased. He also finds that the tensile strength and the 
elastic limit of cold-worked aluminium bronze which had season 
cracked were greater at the edge than at the center. 

In the same year appeared an anonymous article ^ in which the 
author finds that " season cracks in tubing are the results of taking 

2 Diegel, Nachtrcigliches Reissen kaltverdichteter Kupferlegierungen, Verb. d. Ver. z. Bcf. d. Gewerb., 
85, p. 177; 1906. 
* Anoa., Season Cracking in Brass, Brass World, 2, p. 41; 1906. 



Failure of Brass 13 

too heavy 'pinches' in drawing. The specimens experimented 
upon were some hot and cold rolled 10 per cent aluminium bronze. 
The results were as follows: 

1. The hot-rolled bars did not suffer from season cracks. 

2. Although the elastic limit in the cold-drawn bars was greater 
than in those which had been hot rolled, they showed season cracks 
after some time. 

3. The reason for the formation of season cracks is the lack of 
uniform density throughout the metal, as the tests indicated that 
the elastic limit decreased rapidly toward the center. 

4. The density varied in the inverse proportion to the cross 
section. The larger diameters were more apt to crack. The 
average density of the whole cross section and the elasticity of 
the metal appeared to have less influence on the formation of 
cracks than the extreme variation of the density from periphery 
to center. 

5. The formation of longitudinal or cross cracking depended 
on the methods used for drawing the bars." 

Several articles appeared at this time describing instances of 
season cracking and ascribing it variously to the action of ammonia 
vapor;'' to faulty die and punch construction.^ 

An interesting case of the failure by season cracking of brass 
stirring spindles is described by Desch in the discussion of a paper 
on this subject by Milton.' These spindles were used to stir a 
liquid at a temperature near its boiling point; those Avhich had 
not been in service fell to pieces in a short time, whereas those 
of the same lot which had been so used remained sound, the initial 
stresses having been sufficiently relieved at the temperature of 
the boiling liquid. 

Sperry ^ maintains that season cracking can be caused by the 
presence of initial stresses or by the action of mercury or aqueous 
solutions of its salts, and describes failures of this sort which have 
occurred in brass prepared by a mercury salt "dip" for gold or 
silver plating. 

The first one to actually measure the initial stresses, about which 
so much had been said, was Heyn,* who developed methods for 
measuring theses stresses (to be described below) and gave dia- 
grams constructed from such measurements, showing the distri- 

* Season Cracking in Brass Sheet, Brass "World, 6, p. 269; 1910. 

' Anon., Effect of Dies on Season Cracking of Drawn Brass, Mechanical Engineer, 27, p. 159; ign. 
» Milton, Some Points of Interest Concerning Copper Alloys, Journ. Inst. Metals, 1, p. 57; 1909. 
' E. S. Sperry, The Season Cracking of Brass and Other Nonferrous Metals and Alloys as Caused by 
Mercury, Brass World, 8, p. 34s; 1912- 

* A. Martens and E. Heyn, Materialienkunde (iir den Maschinenbau, IIA; 1912. E. Heyn, Internal 
Stresses in Cold Wrought Metals, and some Troubles Caused Thereby, Journ, Inst. Met. 12, p. 3; 1914. 



t4 Technologic Papers of the Bureau of Standards 

bution of the longitudinal or axial stresses in steel and brass rods 
which had failed. He discussed also the conditions of manufac- 
ture under which stresses are produced in worked metals. 

Spontaneous or season cracking occurs in such internally stressed 
objects, according to Heyn, as a result of temperature variations 
of after flow of the metal and particularly as a result of slight 
etching of the surface, which diminishes the section of the stressed 
metal, thereby increasing the stress and causing cracks to appear. 
He gives the results of some experiments to show that these 
stresses are removed from brass rods by annealing at tempera- 
tures (i6o° to 300° C), at which no appreciable softening of the 
material occtus. He also discusses the effect of longitudinal inter- 
nal stresses on the yield point of a metal, and shows that the 
apparent elastic limit of metals may be depressed instead of raised 
by cold work. 

Some later measurements of the initial stresses in brass bars 
were made by Howard.* 

Further articles "> "> ^^' ^^ appearing about this time discuss the 
relation of initial stress to failure, and describe experiences with 
such failures. Von Aken finds in the variation in the micro- 
structure from center to edge of brass rods a sufficient cause for 
season cracking in these materials and recommends annealing at 
1300° F (700° C) as a remedy. 

Guillet " in a general paper calls attention to the possibility, 
among others, of season cracking of high zinc brasses being due to 
the decomposition of the beta phase into the brittle gamma 
eutectoid. 

Finally, Jonson ^^ describes the results of some very interesting 
experiments, showing the effect of combined corrosion and tensile 
stress on the ductility and strength of brass and bronze alloys. 
He studied the effect of subjecting brass to combined stress and 
corrosion with ammonium hydroxide, and draws the following 
conclusions : 

* * * Excessive stress alone does not injure copper alloys, nor does corrosion 
alone or corrosion accompanied by moderate stress. Corrosion, accompanied by pro- 
longed stress, exceeding 20 000 pounds per square inch, is liable to cause cracking in 

» J. E. Howard, Internal Strains in Rolled Brass and Bronze Bars, Trans. Amer. Inst; Metals, 7, p. loi; 

1913. 

'" Anon., Observations and Notes on the Season Cracking of Brass, Brass World, 9, p. 155; 1913. 

M A. B. White, An Investigation of Condenser Tubes; 1914. 

>2 A. D. FUun, Brass in Engineering Construction, Eng. Record, 68, p. 527; 1913. 

u Von Aken, The Cracking of Brasses and Bronzes, Engineering Record, 70, p. 227; 1914. 

'* L. Guillet, Nouvelles Recherches sur les AlUages de Cuivre et de Zinc, Revue de M^tallurgie, 11, p. 1094; 
X914. 

'• E. Jonson, Failures of Porgible Brass Bars, Trans. Amer. Inst. Metals, 8, p. 135; 1914. The Fatigue of 
Copper Alloys, Proc. Am. Assn. for Testing Materials, 40, p. loi; 191s. 



Failure of Brass 15 

any of the above-mentioned alloys. We must therefore regard 20 000 poimds per 
square inch as the practical ultimate strength of copper alloys, and the working stress 
must be taken as a safe fraction of this ultimate stress. 

The following facts seem thus to be established to date: 
(i) Season cracking and similar failm-es occur particularly in 
brasses of copper content of from 60 to 80 per cent, as well as in 
other metals and alloys, such as nickel steel and aluminum. 
W. H. Bassett, in commenting on this point, states that "season 
cracks have never, in the writer's 25 years' experience with 
copper-zinc alloys, occurred in such alloys containing more than 
80 per cent of copper. They are more apt to occur in alloys 
containing lower percentages of copper, because the hardening, 
due to the mechanical working, is more rapid, and the alloys, on 
account of the influence of zinc and other constituents, have an 
initial hardness, due to composition." 

(2) These failures occtu generally only in forged or worked 
metal," and the cracks are found some time after the articles have 
passed inspection, both in service, under load, and even before 
being put into actual service. 

(3) The material after the appearance of the season cracks or 
fractures still possesses good mechanical properties as indicated 
by the tensile and bending tests, including high elongation and 
reduction of area. This is significant in view of the fact that the 
fissures and fractures all occur without appreciable elongation. 

Certain factors seem to favor the development of such cracks. 
These are: 

(i) Temperature variations; it seems to be pretty well estab- 
lished that exposure, particularly to low temperatures, may start 
season cracks. 

(2) The action of air, water, and other corrosive agents on the 
surface of the material. 

The general opinion regarding the cause for brass failures of 
this sort as definitely enimciated by He)ai, although not always 
so clearly stated by others," is that the primary cause is the 
presence of initial internal stresses. The presence of such initial 
stresses has been demonstrated by Heyn and by Howard, and values 
of these stresses determined in materials which have failed, thus 
giving confirmation to this explanation. 

Guillet expresses the opinion that the formation of the brittle 
gamma constituent may be in certain cases responsible for such 

'' Such failures have, however, been noted in "bumed-in" and other castings. 

" The statements that "imperfect die work," "too little annealing," are responsible for this type of 
failure amount in the last analysis to ascribing it to the presence of internal stresses. 



1 6 Technologic Papers of the Bureau of Standards 

failures; he has in mind either the presence of this constituent 
as an actual segregate or in apparent beta, the eutectoid of Car- 
penter. The appearance of such a constituent would embrittle 
the material and cause it to become less resistant to stress. 

From the foregoing it seemed evident that in addition to the 
ordinary tests of the failed materials in question investigation 
should be made of the presence in them of initial stresses and, in 
general, of the relation of magnitude and distribution of internal 
initial stresses to the occurrence of season cracking and similar 
failures in brasses. 

The following questions may be raised: 

(i) What are the characteristics and what the causes of the 
failures which have occurred ? 

(2) What is the relation of the initial stresses to the occurrence 
of failure ? 

(3) Can a safe limit for these stresses be set for different types 
of brass, imder ordinary service conditions, in which the material 
is subjected to both corrosion and external stress? 

(4) What are the stresses to be foimd in new material manu- 
factured to meet high specifications ? 

(5) Can, for a given chemical composition of such material, 
those limits of mechanical properties be ascertained above which 
one may not go in manufacturing brass without leaving the metal 
dangerously internally stressed? It is well rmderstood that, in 
general, a high tensile strength and elastic limit are imparted to 
brasses by cold work, which at the same time leaves stresses in 
the material, so that high ultimate strengths and elastic limits 
may be obtained at the sacrifice of soundness. 

(6) What is the quickest and most convenient method for 
ascertaining whether a material is internally stressed and of 
determining the approximate value of these stresses? 

In addition, therefore, to the failed and other brass materials 
secured through the New York Board of Water Supply, the engi- 
neer's department of the city of Minneapolis, the Navy Depart- 
ment, and the Panama Canal, various samples of wrought brass 
were obtained directly from manufactinrers, investigation of which 
might furnish partial answer to questions 4 and 5. These materials 
are described in detail immediatelv below. 



Bureau of Standards Technologic Paper No. 82 




Fig. 2. — Season cracked brass 

Specimen No. 125 




Fig. 3. — Season cracked ladder side bar 

Specimen Xo. 211 



Bureau of Standards Technologic Paper No. 82 




Fig. 4.' — Fracture 
Material lo X i 




Fig. 5. — Fracture 

Material 35 X i 




Fig. 6. — Fracture 

Material 46 X i 





Fig. 8. — Fracture 

Material 68 X i 



Fig. 7. — Fracture 

Material 6s X i 



Failure of Brass 1 7 

II. INVESTIGATION OF BRASS MATERIALS 

In Table i is given a description of the various samples that 
have been investigated of materials which have been in service, 
together with whatever information is available concerning the 
service conditions to which they, or the lots of material which they 
represent, have been subjected. Unfortunately, this information 
is often verv' meager; indeed, the lack of such information often 
makes impossible the deduction of definite conclusions. 

In Table 2 is given information concerning the new materials 
tested. 

It will be noticed, in considering the failed materials of Table i , 
that several kinds of material are involved, as well as several manu- 
facttirers of the same kind of material. The material has all been 
worked, hot or cold; cast material has seldom been found defective 
in this manner (with the exception of castings repaired by buining 
in). The failure by cracking occurred sometimes merely after 
shipment and storage, and in other cases after having been some 
weeks or months in service under service stresses of widely differ- 
ent values. These cracks or fractures are in all but a very few 
cases transverse or perpendicular to the direction of rolling or 
drawing. Such fissures are shown in Fig. i. In the case of 
large lots of strainer plate, the cracks or fissures were generally 
longitudinal or parallel to the direction of rolling, as shown in Fig. 
2, while the fractures in some bolts were conical in shape or cupped, 
as shown in Fig. 7. The checks in No. 211, Fig. 3, are particu- 
larly interesting, reminding one of the Liider lines. 

The fractures were generally of bright granular or crystalline 
texture (this does not mean the fracture was intercrystalline) , but 
often also of silky texture. Typical fractures are shown in 
Figs. 4 to 8. 

Table 3 gives the results of chemical analyses and physical tests 
of these failed as well as of other brass specimens tested in connec- 
tion with this investigation. The tensile tests were made on a 
specimen machined from the center of the sample, of about 0.5- 
inch diameter and of 2 or 3 inches gage length. 

59850—17 2 



i8 



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vo 


r^ 












o^ 


<j\ 


O O 


o 


o 


CO ** 


■<s- ■* 


•* 1 










«-* 


T-l 


ca 


f^ 


C4 


CQ 


ra 


CM 


OJ 


CM 


CM 


1 



'ti \0 



a 3 



§ 


s 








m 


•s 


^ 




1 


s 


c4 




a 


^ 


o 






Failure of Brass 29 

1. INTERNAL, INITIAL STRESSES 

Initial stresses are introduced into metallic articles in a variety 
of ways. They may be the consequence of the cooling of different 
parts of an object at different rates (shrinkage stresses) , or of the 
cooling at the same rate of a heterogeneous material consisting of 
two or more constituents of different coefficients of expansion. 
They may be the result of unequal degree of plastic deformation 
in different parts of an object, such as in a cold-rolled rod, in 
which the outer layers receive more "work" than the inner ones. 

Their magnitude and distribution may then be said broadly to 
depend upon two factors, one, the "process" factor which includes 
those details of manufacture which determine the rate of cooling 
of materials, the amount and number of reductions in working or 
forging, the temperature at which the work is done, etc.; the 
other, the material factor, those properties of the material, elastic 
limit, ductility, toughness, etc., which determine the degree to 
which materials are sensitive to the manufacturing operations. 
Considering wrought materials, one may cite under the first factor, 
details such as the shape of dies or rolls, amoimt and number of 
reduction between anneals, time and temperature of annealing, 
rate of cooling after annealing or forging, etc. 

The distribution of such stresses may be quite complicated, as 
Howard ^® has shown. When any portion of such an initially 
stressed object is removed a partial relief of these stresses takes 
place through the warping of the object. This warping of cold- 
worked brass upon machining is well known to instrument makers, 
who frequently have to regrind close-fitting parts frequently before 
a permanent fit is secured. The warping due to such stresses 
may occur at least to a slight degree also merely upon standing. 
In constructing a brass plate condenser for precision work. Dr. 
H. L. Curtis, of this Bureau, found that such a condenser made up 
with ordinary hard brass sheet did not possess a constant electrical 
capacity (which depends upon the distance between the brass 
plates), but that the latter kept constantly changing, showing 
that the plates, although well supported, were gradually warping. 
Upon annealing these plates at about 250° F (120° C) no further 
variations in capacity were noticed. 

In the case of wrought rods, particularly as drawn or extruded, 
the distribution of these stresses is simple, as they are radially 
symmetrical. This fact facilitates markedly the measurement of 

i» Loc. dt. 



30 Technologic Papers of the Bureau of Standards 

their value, as it is possible, as H!eyn has shown, to calculate these 
values from the changes in length of such rods during the removal 
of annular cylindrical layers. 

(a) Measurement and Calculation. — ^The stresses measured in this 
way are the stress components parallel to the axis of the rod, and 
may be called the longitudinal or axial initial stresses as distin- 
guished from tangential or radial ones. 

The measurement of the stresses in the brass materials investi- 
gated were made by the Howard-Heyn method.^' In Fi^. 9 is 
shown a specimen after the series of measurements has been made. 
The metal is turned off over the length a; if there is longitudinal 
stress in the layers turned off, these stresses will be relieved and 
the whole bar will elongate or contract. These length changes 
were, in general, measured by means of an end comparator between 
the polished ends of the bar A and B, in some cases, however, by 
line comparator or by strain gage. As the ends, after machin- 
ing, were not perfectly parallel, the same end points or areas had 
to be used for successive measurements; this was made possible 
by scribing lines on the ends: two concentric circles and two 
pairs of parallel-straight lines at right angles, as shown in Fig. 5. 
In this way four areas are given on each end, and the distances 
between each corresponding pairs were measin-ed after each ma- 
chine cut. The value taken was the average of these four unless 
otherwise stated. In this way correction was made for any eccen- 
tric distribution of the stresses. 

It was found that certain precautions were necessary in machin- 
ing the specimen. It was necessary to take a light cut for two 
reasons, first, in order that the temperature of the specimen might 
not rise too much during machining, and second, in order that 
there should be a minimum possibility of introducing stresses at 
the surface of the machined bar by the tool pressure. A cut of 
0.005-inch feed and lead was practically uniformly adhered to, 
with a speed of about 500 r.p.m. (60 to 125 linear feet per minute). 

The temperature of the surface near the tool was not allowed 
to become so warm that the hand could not be kept on it, and the 
bar was cooled with an air blast or water when the temperature 
threatened to go above this point. Thus was prevented the possi- 
bility of any annealing action going on during the machining. 

It was noticed in the preliminary experiments that the use of 
the ordinary form of dog in gripping the specimen on the lathe was 

" Such measurements were first made on Harveyized steel bar by Howard (tests of metals, Water- 
town Arsenal, 1893, p. 285); Heyn independently developed the method i arther. Martens-Heyn, 
Handbuch der Materialienlcunde, loc. cit. 



Bureau of Standards Technologic Paper No. 82 



B 




Fig. 9. — Form of specimen used in measuring initial stress 




Fig. 10. — Specimen for rapid initial stress test 
on bars 



Failure of Brass 31 

not advisable, as the compression of the specimen by it caused in 
itself an appreciable elongation. It was necessary to use a special 
device, which consisted of a piece of one-fourth inch steel wire 
bent to a right angle. One arm was bolted to the face plate 
of the lathe and the other went through a transverse hole in one 
end of the brass specimen and was lightly secured therein by bolts. 
This arrangement, it was observed, introduced no errors in the 
measurements. 

The length AB oi the specimen over which it was turned down 
varied from 5 to 25 cm. 

The stresses in each layer were calculated from the formula " 

E dl{\^-h)-dl, (ln_,-lo) 



5 = 



1' dl,-dl 



A consideration of the sources of error of such measurements 
shows that there are three principal kinds : 
(i) Errors due to temperature variation; 

(2) Errors in length measurements on the comparator; 

(3) Errors in the determination of the modulus of elasticity. 
The error due to (i) was very small as care was taken to secure 

a uniform temperature over the specimen and to measure this 
temperature to 0.1° C. The probable error in the length measure- 
ments was about 0.3 to 0.5 y, (about 0.000012 to 0.00002 inch). 
This corresponds in the majority of cases to a probable stress error 
of about ±300 to 500 poimds per square inch, although in a few 
cases where short lengths were taken this error would be from 
±600 to 1000 pounds per square inch. The probable stress error 
is directly proportional to any possible error in the modulus which 
is probably about ±3 per cent. The total probable error in any 
one measurement can be assumed to be about ±3 to 4 per cent. 
In a few cases the specimens were too small or irregularly shaped 
to be turned in a lathe, and in these cases the metal was etched 
off with dilute nitric acid and the length measurements made with 
a line comparator. In such cases the error due to irregular cross 
section, etc., may have been much greater, as much, possibly, as 
50 to 100 per cent. 

" Where S= stress 

E=the modulus of elasticity 

1'= length over which the specimen is turned down 

<fn= diameter of turned down part after the nth machine cut 

ln=length of bar after nth machine cut 

Io= original length of bar 
A plus value for S indicates a tensional stress in the corresponding layer. 



32 



Technologic Papers of the Bureau of Standards 



In several cases a strain gage was used, in which cases the prob- 
able stress error due to a lesser accuracy of the length measure- 
ment may have been 5000 pounds per square inch. 

In some cases the value of E could not be determined on the 
same bar which had been used in the determination of initial 
stress, and the value of E of other samples of the same lot had to 
be used. This introduces an unknown error which probably will 
not exceed at the maximum ±12 per cent. 

Values obtained from measurements made imder the less favor- 
able conditions of this sort will be indicated in the tables below. 

There is obtained by such measurements a value of the internal 
stress for each annular or rectangular layer, which may best be 
presented in the form of diagrams in which the stresses for each 
layer are plotted as a function of either the diameter ^^ of the 
annular layer, or of this diameter squared, as Heyn has done. 
For convenience in obtaining average values of the initial stresses 
we have chosen to use Heyn's method and plot the stresses as a 
fimction of the diameter squared. 

Such a diagram is given in Fig. 97 for M 3. The outer layer of 
this 1.25-inch rod was in tension from the edge, at a diameter of 
-v/i-57 = i-25 inches, to the neutral point, which lay at a diameter 
of -y/o-82 =0.905 inches. The average value of that tension was 
25 000 pounds per square inch, the maximum value, 44 000 poimds 
per square inch. From the neutral layer to the center the metal 
was in compression. 

TABLE 4 

Initial Stress Measurements Made on Different Samples of the Same Manganese- 
Bronze Rod 





Distance 

of sample 

liom end 

of bai 


Length 

of 
sample 


Method ot 
procedure 


Initial stresses 


B. S. No. 


Average stress 


Maximum 
tension 


Maximum 
compression 


136-2 

136-24 

136-50 

136-51 

136-0 

214-1 


Feet 


10 
14 
14 
11 


Ins. 

6 





2i 




Inches 
5 
5 
2i 
10 
5 

10 
10 


Turning down. 

do 

do 

do 

Boring out 

Turning down. 

Boring out 


lbs./hi.2 
22 200 
22 000 
25 000 
22 800 

20 500 
22 500 

21 300 


kg/cm2 
1560 
1540 
1750 
1600 
1440 
1580 
1490 


lbs./in.2 
34 000 

36 000 
38 000 
38 800 
22 800 

37 500 
30 200 


kg/cm> 
2390 
2530 
2670 
2730 

' 1610 
2630 
2120 


lbs./in.> 
32 000 
32 000 
34 000 
29 300 
36 600 
23 400 
29 500 


kg/cm» 
2250 
2250 
2390 
'2O6O 
2580 
1640 


214-2 






2050 











(b) Values of Initial Stresses. — Diagrams are shown for typical 
materials tested in Figs. 97 to 120. 

^ For rectangular or square rods one would use one transverse dimension in place of the diameter. 



Failure of Brass 33 

In order to ascertain what agreement could be obtained in the 
measurement of these stresses on the same material by different 
methods and over specimens of different length, several measure- 
ments were made of these stresses in specimen M 136, a 20-foot 
length of I -inch diameter manganese-bronze round rod. The posi- 
tion and length of these samples, the method of procedure in 
machining, and the results of the measurements are given in 
Table 4, and an idea of the agreement between the results of these 
tests may be obtained from the initial stress diagrams, Figs. 103 
to 1 10. It is seen that although individual layers will often possess 
stresses of different value in different parts of the rod, the average 
value of the stresses agrees very closely, as can be seen by reference 
to the table below. In particular, these results indicate (i) that 
the results by boring out and turning down are almost identical, 
with the precautions observed, (2) that the end effects -- are 
limited to a very small length at the ends, since the values of the 
stresses on adjacent samples of lengths 2^ and 10 inches, respec- 
tively, show good agreement. In fact, the average stress in the 
small specimen, M 136-50 is greater than in the adjacent lo-inch 
sample. No. 136-51, which is the reverse of what would be ex- 
pected if the stresses were much lower near the ends of the test 
specimen. 

Another set of determinations was made on adjacent lo-inch 
length of 2 -inch diameter round Tobin bronze rod, in order to 
determine what agreement would be found between the results 
obtained by machining down and by boring out a rod. These 
results are also given in Table 4 and in the stress diagrams Nos. 1 09 
and 1 10. Apparently the variations in values are within the limits 
of experimental error or of the variation of uniformity of the bar 
itself. 

Although the initial stress diagram alone completely describes 
the state of initial stress (as regards longitudinal stresses) in a bar 
or rod, it is possible to choose certain values of these stresses which 
may serve as at least approximate characteristics. Such are the 
maximum tension, the maximum compression, the stress value in 
the outermost layer, and the average stress (without regard to 
sign). The maximum values are not generally conveniently 
possible of accm^ate determination, for the reason that these 
maxima are attained in a very thin layer only of the material, 

2* Dr. G. R. Olshausen has suggested that at the ends the stresses must be zero in value, and the actual, 
original value (i. e., before the bar was cut at these ends) of the stress in any layer is reached only at some 
distance from the ends. What is measured is an average value, over a length of rod which may include a 
part of the rod near the ends in which this variation of str^s is taking place, 

59850—17 3 



34 



Technologic Papers of the Bureau of Standards 



which layer is included together with adjacent ones, containing 
lower stresses, in the larger one machined off. It would be neces- 
sary, in order to determine maxima accurately, to take infinitely 
thin steps in machining. 

The Table 5 contains these four principal values of the initial 
stress in each specimen tested. A column indicates which kind of 
stress exists in the outer layer (C= compression, T = tension). 

TABLE 5 

Principal Values of the Initial Longitudinal Stresses in Brass Materials 

[Conversion factor, Ibs./in.^ to kg/cm2 0703] 



B. S. No. 


Average 
stress 


Maximum 
tension 


Maximum 
compression 


Stress in 
outer layer 


T=Ten- 

sion 
C= Com- 
pression 


Remarks 




lbs./in.2 


lbs./in.2 


Ibs./in.2 


lbs./in.2 






2 


18 800 
25 000 
18 400 


60 500 
44 000 
28 400 




60 500 
32 000 
27 500 


T 
T 
C 




3 


33 000 
28 200 




22 a 




23 a, 6 


15 400 


24 500 


31 600 


18 000 


C 




28 a 


5500 


7500 


8500 


8430 


C 




32 a 


17 900 


20 500 


26 500 


26 400 


C 




34a 


18 700 


26 500 


25 500 


16 000 


C 


Material of which from 4 to 83 


41a 


4400 


32 000 


5500 


5600 


C 


per cent failed in service. 


43 a 


2500 


4500 


5500 


400 


C 




49 a 


3100 


3500 


7000 


6500 


c 




54 a 


1600 


5000 


6500 


5100 


T 




67a 


6400 


12 000 


11 000 


12 400 


T 




68 «> 


3900 


7500 


9000 


5500 


c 




74 c 


15 700 


17 000 


21 500 


9800 


c 




78 c 


9500 


29 500 


6500 


29 600 


T 




83 


1000 
2000 
750 
750 
1870 
2300 
9900 
8500 
4300 


2500 
7000 
1250 
2000 
8000 

13 300 
7500 

46 000 
3500 


1500 
6000 
1000 
1200 
2000 
5800 
15 000 
19 500 
5500 


2700 

1400 

1400 

2000 

8200 

13 000 

15 000 

46 000 

5800 


T 
T 
T 
T 
T 
T 

c 

T 
C 




85 




92 




94 


New material. 


101... 




103 




116 c 

118 c 

125 c 


About 20 per cent failed in 
service. 


129 


14 600 
17 600 


20 000 
19 500 


24 000 
59 000 


22 000 
59 000 


C 
C 


New material. 


131-L 




131-T 


1500 


5500 


2500 


5600 


T 




136 6 


22 200 


34 000 


32 000 


27 000 


T 




ISSc 


500 


2500 


450 


2500 


T 




140C 


18 000 


46 000 


42 000 


46 000 


T 


20 per cent failed. 


142c 


30 300 


29 500 


70 000 


29 200 


T 




156. 


3000 
3100 


15 000 
5100 
43 000 
84 000 
53 000 


11 500 
7700 


15 000 

6000 

9000 

83 000 

26 000 


T 
T 
T 

T 
T 




157 




158 


From lots of failed material. 


160 


30 300 


38 700 




161 <« 





a The determination of E was made on samples of the same lot, but not on bolt tested for initial stresses. 
*> These materials had nonsymmetrical stresses over 2000 to 3000 pounds per square inch. (See p. 36.) 
' The value of E was assumed to be 16 000 000 pounds per square inch. 
"J The value of E was assumed to be is 000 000 pounds per square inch. 



Failure of Brass 
TABLE 5— Continued 



35 



B. S. No. 


Average 
stress 


Maximum 
tension 


Maximum 
compres- 
sion 


Stress in 
outer layer 


T=Ten- 

slon 
C= Com- 
pression 


Remarks 


162 


lbs./ln.= 
2750 
2900 

12 000 
9«0 

13 100 
32 600 

3500 
42 500 
6600 
15 700 
4200 
37 500 
3380 
5600 
2400 
1100 
1100 
3800 
1900 
2000 
5620 
5270 
7700 
3600 
5200 
3400 
1950 
5500 
5400 
4900 
5500 
3630 
5300 
2280 
4400 
1100 


Ibs./in.2 

6000 

3000 

14 000 

9600 

17 500 

56 500 

5100 

94 000 

11 900 

32 500 

6100 

65 500 

9000 

9000 

4300 

3000 

3700 

5000 

3000 

1700 

6500 

7500 

9800 

4500 

6000 

3200 

3200 

4500 

7800 

7200 

6000 


lbs./in.2 

15 500 
11 500 
33 000 
26 000 
28 000 
44 500 

6000 
44 000 
10 000 
22 500 

10 800 
53 500 

9000 
8400 
5800 
3000 
1500 
8000 
4500 
6500 
14 000 

11 800 

12 000 
4500 
8000 
5500 
2S0O 
7000 
9200 

11 700 
9300 

11 200 
8700 

35 600 

16 100 
5400 


Ibs./in.^ 

7000 
1000 

11 000 
27 000 
26 000 
56 000 

7000 
42 000 

10 000 

12 000 

11 000 
40 000 

8000 
9000 
2500 
3500 
2000 
8000 
4500 
5000 

13 000 

12 000 
12 000 

3000 
8000 
3000 
2000 
4500 
7500 

12 000 
4000 

11 200 
8700 

35 600 

16 100 
5400 


C 
C 
C 
C 
C 
T 
C 
T 
C 
T 
C 
T 
C 
T 
T 
T 
C 
C 
C 

c 
c 
c 
c 
c 
c 
c 
c 

T 
T 
C 
T 
C 
C 
C 
C 
C 


1 


163 


Material did not (ail. 


164 




165 




166 




167 




168. . . 




169 6 

170 


New material. 


171 

172 




173 




174 




175 




181 

182 

183 

184 

185 




186 


Brass bolts, representing lots 
' of some 1000-1500 tiolts which 


187 


188 




189 




193 a 

195 

197 a 

199" 

201-A<: 

203 




204 


New material. 


205» 

235 




244 


9850 
6900 




245 6 

246 


Failed material. 


247 . 













• o The determination of E was made on samples of the same lot, but not on bolt tested for initial stress, 
!> These materials had nonsymmetrical stresses over 2000 to 3000 pounds per square inch. (See p. 36.) 
' The value of E was assumed to be 16 000 000 pounds per square inch. 

A very wide variation, both in magnitude and in distribution of 
these initial stresses, is noticed from the table, corresponding to the 
variation in the countless details of manufacture. 

The distribution of the initial stresses is interesting and gives 
an indication as to the mode of manufacture of the material. 
Drawing cold introduces tension on the outside and compression 
on the inside, whereas extrusion produces the reverse effect. The 
rods Nos. 3, 136, 160, 167, and 173 have been finished by heavy 



36 Technologic Papers of the Bureau of Standards 

cold drawing, whereas the work done on the others was largely 
extrusion followed by a draw to size. The effect of this final draw 
can always be seen in the displacement of the stress values at the 
surface toward tension. In some cases — for example, No. 67 — 
the final draw has been sufficient to neutralize the compression at 
the surface resulting from extrusion and produce actual tension ; in 
others — Nos. 32, 43, 164, etc. — the final draw has only succeeded 
in partially neutralizing these surface compressionaj stresses. 

(c) Radially Nonsymmetrical Stresses. — It was noticed in the 
measurement of the length changes which took place upon 
machining that these were not always the same in value for the 
four positions. In the great majority of cases these differences 
were small and could be explained by a slight inaccuracy in center- 
ing the bar for machining, such that the layers turned off were not 
concentric to the true center of the rod. In some cases these 
differences were, however, too large to be accounted for in this 
manner and were due to an eccentric distribution of stress which 
can be approximately described as consisting of a system of radially 
symmetric stresses superimposed upon two sets of initial resisting 
moment stresses, referred to two neutral diametral planes at right 
angles to each other. These latter may be looked upon as initial 
bending stresses, and their values were calculated in the cases in 
which a great variation in the elongation or contraction along 
opposite fibers gave evidence that they were of large value. 

In so doing use was made of an equation^^ similar to the one 
on page 31, and which is given below. 

E (dn-i + dn) r ,4 .jA _jc \_J4 nA_lC.-i 

"^^ 4 L>1 ((i*_i-£^n)'- ' ^ ' '^ ^^ ^^■' 

This equation was derived by considering that the specimen is 
built up of concentric annuli of differing unit stresses, hence of 
differing resisting moments, which, however, in summation equal 
zero; expressing this fact 



v^l Lj L-n C-„ 



>3 Where 

SB°-average fiber stress in nth layer contributing to a resisting bending moment only. 
E-»the modulus of elasticity. 
£><= transverse distance between opposite pair of points A and B (i. e., i and 3 or 3 and 4 in Pig. 5) on 

ends of bar, at vrhich length measurements were made. 
l'=lengtbof bar. 

</!!■= diameter after nth machine cut. 
.A| 

Total elongations of bar after the removal of the nth layer at the points A and C. respectively. 



'n 



Failure of Brass 37 

Where 5 is the liber stress at a distance C, and /, the moment of 

inertia of the section . The subscripts refer to the successive layers 

57' 
or annuH, and the term -^ to that cyHndrical part of the bar 

^ n 

remaining after turning off the nth layer. 

E C 
Considering now that Si = „ ° 

where R is radius of curvature of bar originally straight, and is 
equal to 



1A C 

»n— In 



using the proper values for / and combining the above equations, 
the full equation is obtained. 

Although these stresses as so measured were of little significance 
in the majority of cases, as mentioned above, amounting to in 
maximum ±1000 pounds per square inch, mention is here made 
of them and the measurements made of them to show that a false 
impression of the longitudinal initial stresses may be obtained by 
noting the average change of length only in such measurements. 
In materials Nos. 23, 136-2, and 169 such bending (fiber) stresses 
were found amoimting to at maximum ±16 800, ± 8000, and ± 1 8000 
pounds per square inch, respectively.** These stresses must be 
added algebraically to the average longitudinal fiber stresses in 
order to obtain the true stress at any points. These bending 
stresses of large value are probably introduced into the rods during 
straightening. 

(d) Rapid Methods for Initial-Stress Determinations. — The im- 
portance of having methods, which are quick and convenient, by 
which materials may be tested for the presence of internal stresses 
will at once be realized. The layer-by-layer method is the only 
accurate one as yet known, but it is much too slow for inspectional 
work, for example. 

Instead of so measuring the stresses the average value only 
may be measured, only one layer being removed by machining in 
this case, of which the area is equal to 0.5 of the total area. In 
the great majority of cases the initial stress changes sign at about 
that value of the diameter — that is, 0.7 of the original diameter — 
at which the remaining cross-sectional area is 0.5 of the original. 
A strain gage can be used in this case, with gage points on two 
opposite fibers. For an 8-inch gage, for example, the specimen 

'* The presence of such nonsymmetrical stresses of significant value is noted (6) in Table 5. 



38 Technologic Papers of the Bureau of Standards 

should be lo inches long; if a layer 7 inches long is removed, the 
average stress would be 



E(dl (l„-lo) \ 
I'V dl-d^ ) 



= f(ln-]o) 

7 • 

A stress value of 2000 pounds per square inch would give a 
change in length of 0.00 1 inch. 

A second method of obtaining a value of the initial stresses was 
suggested by S. W. Milieu, of the Rochester & Mohawk Welding 
Works, and tested by us on samples of known initial-stress distri- 
bution. This method depends upon the fact that a portion cut 
longitudinally from a round rod, and having a sector section 
similar to that in Fig. 10 will bend, such that the outer surface, 
originally straight, will be convex or concave, depending upon 
whether compression or tension were originally present in the out- 
side layers. In Fig. 10 is show^n specimen M-i 36 with such a section 
of 30° angle removed over a length of 5 inches. The concave 
curvature of the piece removed is easily seen. 

Making the assumption that bending takes place around a 
neutral plane passing through the center of gravit}^ of the section, 
there can be calculated the change of the stress in either outside 
original surface fibers or inside original ones caused by the bending. 
These are, respectively, 

_£r_8£:§r 

„ _ 2Er 1 6E 8r 

where 

ASo, A5i == changes in stress at outer and inner fibers, respectively. 

E = modulus of elasticity. 

7? = radius of curvature produced by bending. 
5 = bending at center in linear measure. 

L = length of specimen. 

r = radius of rod. 
Three 5-inch specimens were so tested and the results so calcu- 
lated are compared in Table 6 with those obtained by the com- 
parator method. The assumption is further made in this table 
that the larger fraction of the initial stresses is released by the 
bending, such that the calculated change in stress is equal approxi- 
mately to the original stress. Naturally these assumptions hold 



Failure of Brass 



39 



the better, the nearer the actual initial stress distribution corre- 
sponds to a linear one with a change of sign of stress at the neutral 
axis passing through the center of gravity. 

TABLE 6 
Comparison of Measurements of Initial Stress by Two Methods 



B. s. No. 



136 
168 
169 



Initial stresses " as measured by 
comparator method 



Average 
stress 



lbs./in.2 

22 250 

3500 

42 500 



Maximum 

stress near 

surface 



Ibs./in." 

+ 34 000 
- 6000 
+94 000 



Maximum 

stress near 

center 



Ibs./in.' 
-32 000 

+ 5100 
-44 000 



Amount of 
bending 
at center 
of 5-inch 
specimen 



inches 

0. 0350 
.0510 
.0059 



Initial stresses " by 
release-bending method 



Outer 

surface 



lbs./in.2 

+ 30 000 
- 4720 
+ 41 000 



Inner edge 



lbs./in.2 
-60 000 
+ 9400 
-82 000 



" The signs refer to the kind of stress; + signifies tension. 

From the table it is seen that for these materials there is good 
agreement between the maximum stress values at or near the 
outer surface, but not at the center, where the release -bending 
method gives them uniformly too high. This test is recom- 
mended as being the quickest method known of obtaining an 
approximate idea of the value of the initial stresses. 

One must not overlook in these last two methods described 
their inherent faults. It is possible to obtain false results by 
both methods when the initial stress changes sign more than 
once and by the Miller method when the stress distribution dififers 
widely from a linear one, with neutral point at a distance from 
the center equal to 70 per cent of the radius. Some sacrifice in 
accuracy must be made when rapidity and ease of manipulation 
are desired. 

(e) Removal of Initial Stresses by Annealing. — Experiments 
were made to ascertain under what conditions of annealing the 
initial stresses could best be removed. From one manganese- 
bronze material, No. 136, of which a 20-foot length of rod was 
supplied, several 5 -inch lengths were taken and annealed for 
different periods at several temperatures. Initial stress measure- 
ments and tensile tests were then made on the specimens so 
treated. 

The Table 7 contains the results so obtained. The initial 
stress diagram for 136-6, annealed for one hour at 400° C, is 
given also in Fig. 108. The values given in the Table 7 of the 
average initial stresses are plotted in Fig. 11 as a function of the 



40 



Technologic Papers of the Bureau of Standards 



annealing temperatures. It is seen (i) that temperatures of 
from 300° to 400° are sufficient to reduce in from one to seven 
hours the initial stresses to a safe value, and (2) that annealing 
for from one to seven hours at 400° C does not soften this material 
in the sense of reducing either the ultimate strength or the pro- 
portional limit. It is thus possible to anneal this brass material 
in such a manner as to remove the internal stresses and yet not 
affect the mechanical properties. No significance is probably to 
be attached to the initial rise of curve No. i in Fig. 11. It is prob- 
able that the original average stress in this sample was actually 
higher than that of the two original samples tested. 

TABLE 7 
E£fect of Annealing on Properties of 1-inch Manganese-Bronze Rod 



B. s. No. 



136-2. 
136-24 
136-8. 
136-16 
136-3. 
136-17 
136-9. 
136-12 
136-20 
136-10 
136-18 
136-6. 
136-14 

23 

23A.. 



Time of 
annealing 



Hours 

(") 
(«) 



(a) 



Tempera- 
ture of 
annealing 


Average 
stress 


°c 


Ibs./in.' 


(«) 


22 250 


(«) 


22 200 


100 


24 700 


100 


18 250 


110 


16 800 


170 


17 200 


170 


11 400 ' 


232 


5500 1 


232 


3100 j 


360 


1470 j 


360 


150 


400 


1200 


400 


100 


(") 


15 400 


^00 


3000 



Maximum 
tension 



Maximum 
compres- 
sion 



lbs./in.2 

34 000 

36 000 

31 400 

65 000 

29 000 

29 000 

17 500 

8100 

3500 

5000 

1000 

5600 

100 

24 500 

U 000 



Ibs./ln.i 

32 000 

32 000 

38 500 

35 000 

24 300 

23 500 

16 600 

7000 

SOOO 

1500 

200 

1000 

500 

31 600 

16 500 



B. S.No. 


Time of 
annealing 


'ff,^P«"-; Ultimate 
annealing 1 strength 


Propor- 
tional 
limit 


Elongation 
in 2 inches 


Seduction 
ot area 


136-4 


Hours 

1 

7 


"C ■ lbs./in.2 

(") 72 000 
400 72 500 
400 71 000 


Ibs./in.2 

27 500 
35 000 


Per cent 

44 
3i 


Per cent 
50 


136-7 


49 


136-15 


32 500 37 


50 













" As received . 

This material was not an extremely hard manganese bronze, 
and it is probable that in the case of brasses whose "work hard- 
ness" is much greater, such as No. 173, the elastic limit will be 
affected at lower temperatures than 400° C, and annealing even 
below that temperature will soften the material. It is, in fact, 



Failure of Brass 



41 



possible that an inverse relation exists between the work hardness 
of the bronze and the temperature at which plastic flow begins 
under the influence of initial stress. However, this brass tested, 
No. 136, was as hard after annealing at 400° C as is ordinarily 
specified for manganese bronze and much harder than is required 
by the New York Board of Water Supply specifications, for 
instance. 

It is interesting to notice that the stresses in the specimen 23 A 
were not so completely removed by annealing at 600° C for one- 
half hour as those in No. 136 by annealing for one hour at 300° 
to 400° C. 



o 



CO 

M 
ft 



00 



30000 



30000 



10000 















\l 










3\ \ 












W 


=1^ 





100 



300 



300 



400«'C 



Fig. II. — Effect of annealing on the average initial stresses in a manganese bronze 

Abscissas ; Atmealing temperatures in "C 

Ordinates : Average initial stress in iwunds per square incli 

Curve I For i hour's annealing 

Curve 2 >..... For 7 hours' annealing 

It should here be emphasized that the results on the small 
I -inch diameter rods, which were used in these annealing experi- 
ments, can not necessarily be taken as numerically characteristic 
also of heavier samples, for which higher temperatures and longer 
periods of heating are probably necessary in order to relieve the 
stresses. 

In connection with the annealing of brass in order to relieve 
initial stresses, it may be mentioned that a whole filter in the city 
of Minneapolis filter plant was equipped with annealed plates and 



42 Technologic Papers of the Bureau of Standards 

bolts -^ and put in operation on February 15, 191 5. To date, 
August, 1 91 6, no breakages have been experienced in this filter, 
although the conditions are otherwise the same as those under 
which the failures described on pages 8-10 occurred. This experi- 
ence indicates the practical effect of relieving the initial stresses in 
brass by annealing. 

2. STRUCTURE OF BRASSES AND ITS RELATION TO FAILURES 

In Fig. 1 2 is reproduced part of the equilibrium diagram for the 
copper-zinc alloys according to Carpenter.^* Alloys containing 
up to about 37 per cent of zinc are homogeneous in structure and 
consist of the solid solution known as alpha. Alloys of compositions 
37 and 47 per cent are heterogeneous and consist of mixtures of alpha 
and apparent beta, according to Carpenter, or beta prime, according 
to Hudson. Carpenter believes that the beta constituent breaks 
down into a eutectoid of alpha and gamma at 470° C, this eutectoid 
being in general of so fine a state of division that it appears as a 
homogeneous constituent. Hudson,^' on the other hand, claims 
to have proven that the beta suffers merely an allotropic modifica- 
tion at 470° C, forming what he calls beta prime, a constituent 
which differs apparently in no sensible manner from beta. The 
authors will refer in general to the apparently homogeneous con- 
stituent which occurs together with alpha in 60 : 40 brasses as beta. 

The tin-copper equilibrium diagram is quite similar to Carpen- 
ter's zinc-copper one, and the alloys show the same phase changes, 
except that there is a visible transformation of beta into a eutectoid 
of alpha and gamma. When tin is added to a copper alloy it dis- 
solves in either or both of the solid solutions up to a certain extent 
and acts structurally very much like an addition of about 2.5 times 
that of zinc. For the sake of convenience one can then, from the 
structural standpoint, consider that a brass containing tin in not 
too large amounts is simply brass witli^ a fictitious zinc content 
higher than its actual one by 2.5 times the content. If too much 
tin is added, depending upon the percentage of zinc present, a 
third constituent, the so-called delta constituent, appears. 

Considering all such brasses, as Muntz metal, Naval brass, and 
Manganese bronze in this Way, the shaded strip in the Fig. 1 2 
represents the range of compositions (fictitious zinc compositions) 
usually met. For instance, a manganese bronze (copper, 56.89 

'» These were annealed for an hour or two at 700° C (1300° F) and cooled very slowly under lime. 
" H. C. H. Carpenter, Further Experiments on the Critical Point at 470° C in Copper-Zinc Alloys; Journal 
of the Institute of Metals, 7, p. 70; 191 j. 
'■ O.F. Hudson, TheCriticalPointat46o°Cin Zinc-Copper Alloys. Journ, Inst, of Metals, 12, p. loi; 19M. 



Failure of Brass 



43 



per cent; zinc, 40.53 per cent; tin, 1.17 per cent) would be an alloy 
of 40.53 + (i. 17 X 2.5) =approximately 43 per cent fictitious zinc 
content. 

The lead and the manganese usually found in these alloys 
(manganese onlv in manganese bronze) are present in very slight 
quantity and are generally dissolved in the two constituents, hence 



The COPPER-ZINC Equil ibr i\i». Diagram 
. . Carpenter ... 


1000 
900 

u 800 

< 

t: 700 

b) 



g 600 

% 

PC 

S 500 

s 

400 
300 




^^ 






'<^ 










1832 
1652 
1472 e^ 

Ed 
■X 

1292 1 

b. 

1112 S 
932 " 
752 
572 




\ 


\ 


\ 


1 














a 


\\ 


X 


:::: 


/ 












V 


% 


< 

e- 

M 


/ 








ALP 


H A 




Z 


:/ 


















1 


V 














e 




;? 


1 










^ 


d 














1 


















1 










10 20 30 40 50 60 percent ZINC 
COMPOSITIOlf 



Fig. 12. — Portion of the Cu-Zn equilibrium diagram according to Carpenter 
The shaded strip represents the range of compositions of brasses investigated 

are not visible microscopically. The iron in manganese bronze may 
apparently either be dissolved in either alpha or beta or both, 
hence microscopically invisible, or it may be present as such in the 
form of fine gloVjules. 

It is then to be noticed that, in general, brass of this tyj^e should 
consist of beta grains inside of which the alpha has separated 
during cooling. If extensive work has been applied below the 



44 Technologic Papers of the Bureau of Standards 

line bd, of the separation of alpha, this constituent may be expected 
to show in its distribution the effects of that work. In the case of 
rolled or drawn material, particularly if worked and annealed 
repeatedly, this distribution takes the form of parallel rows of 
elongated alpha and beta grains. 

If, however, the work has been applied above the line bd the 
alpha constituent forms after the work has been done and hence 
shows no effect of this work, whereas the beta grains may be 
elongated. 

Both of these types of structures are found in brasses of this 
type. 

Of each of the specimens a three-fourths-inch longitudinal 
central section — that is, a center section parallel to the direction of 
rolling or axis of the rod — was prepared and etched. This was 
taken immediately adjacent to the fracture in the case of the frac- 
tured specimens and taken so as to include one or more fissures in 
the case of the cracked or fissured materials. These specimens 
were first heavily etched to show the macrostructure, and then repol- 
lished and lightl}^ etched to show better the microstructure. 
Heavy etching of these alloys is best accomplished Avith an am- 
moniacal solution of copper-ammonium chloride: 

Cu-Am-0H-(2) 5 gr. copper ammonium chloride 
5 cc cone, ammonium hydroxide 
I20 cc water. 

This reagent will develop nicely the beta grains, but for the pur- 
pose of developing the microstructure satisfactorily recourse may 
be had to a more dilute solution of (2) such as: 

Cu-Am-OH-(i) 5 gr. copper ammonium chloride 
7.5 cc cone, ammonium hydroxide 
1000 cc water. 

The reagent etches the alpha constituent dark in general. 
However, a queer fact was noticed in this connection, namely, 
that a specimen in which the alpha would etch dark at first would, 
after a period of several days, etch exactly in the reverse manner 
with the same reagent; that is, with alpha light. The authors 
are inclined to look upon this phenomenon as being due to the 
release at the surface of initial stresses, which alter the relative 
corrodibility (electrolytic potential) of the beta and alpha con- 
stituents. 

In some cases a light etch with ammonium hydroxide with 
hydrogen peroxide is more satisfactory, or a polish attack with 
ammonium hydroxide. The latter etches beta dark in general. 



Failure of Brass 45 

A number of figures axe given showing the typical macro- and 
microstructures of these brasses, and the Table No. 10 gives 
information concerning these. The direction of the axis of the 
rod or of the rolling or drawing operation is in all cases when 
not otherwise noted vertical on the page. 

The Figs. 14 to 35 show the macrostructures of typical samples 
of brass. In most cases the beta grains can be seen, which vary 
greatly in size and are often elongated in the direction of rolling 
(see Figs. 25, 26, and 27). In other cases. Figs. 24, 29, 17, and 
19, no traces of these grains can be noticed. In the case of speci- 
men M-19, Fig. 16, the beta grains are fine elongated at the 
center and large polygonal at the edge. This illustrates the fact 
that recrystalhzation takes place more rapidly the greater the 
deformation undergone, which has been greatest at the surface 
in this case. This is the only case found of such a structure, 
except in the upset bolt heads, materials Nos. 60, 193, 197. 

In the case of rivet head M-ii, Fig. 15, the beta grains are 
surroimded by an alpha envelope; this material has been over- 
heated in forging and is brittle, the fracture following the grain 
boundaries. Such intercrystalHne fracturing or fissiuing is very 
rare except in overheated material and was found only in these 
few cases «f the rivet heads M 10 and 1 1 and in some brass plate 
M-131, which had been bent hot and evidently overheated in so 
doing. The fissures formed differed from ordinary season cracks 
in that they follow the crystal boundaries. This is shown in 
Fig. 96. A careful study was made of the structure at the frac- 
ture or near fissures in failed specimens in order to determine 
what the relation was, if any, between the structure and the 
fissm"e and to detect also traces of overheating. It was claimed, 
for instance, that the heads of the failed bolts from the Panama 
Canal had been biurned. In no case, with the exception of speci- 
mens ID, II, and 131, was the fracture intercrystalHne. The 
fissures or Hne of fractiure crossed the beta grains and the alpha 
particles indiscriminately, often changing direction somewhat as 
it passed from one beta grain to the next, but never seeking out 
the grain boundary. This is illustrated in Figs. 89 to 96. This 
fact is interesting in view of the fact that cracking of this type in 
alpha brasses, cartridge brass, etc., is almost imiversally inter- 
crystalline. 

With reference to overheating it was found that none of the 
specimens except the rivets 10 and 11 and possibly the plate 131 
had been overheated. No traces of overheating were foimd in 



46 Technologic Papers of the Bureau of Standards 

the specimens from the Panama Canal. It should be pointed 
out in this connection that the term "burnt" applies only to 
metal which has been heated to incipient fusion, such that cohe- 
sion between the grains has been destroyed. The term is often 
used when "overheated" is meant. 

Interesting are the macrostructures of the upset bolt heads, 
Figs. 20, 32, and 34, which show the effect of the work done on 
them in initial deformation of structure and in the recrystalliza- 
tion; the latter is more pronounced at top and sides than in the 
center, which is most probably accounted for by the fact that at 
these points greater deformation has been undergone by the 
material, which has therefore recrystallized here more rapidly. 

The typical microstructures of the brasses are shown in Figs. 
36 to 88. In many cases two are given for each specimen, one 
taken at the center and one at the edge (such that the center of 
the figure is i mm from the edge) . 

The two types of structure which were mentioned above are 
illustrated in Figs. 45-46, 36-37, and 69. These two types 
will be referred to as the linear and nonlinear structure, respec- 
tively. The former is found in naval brass, Muntz metal, and 
similar compositions, and but rarely in manganese bronze. An 
example of it in the latter material is seen in the case of material 
197, Fig. 82. The structure of the manganese bronzes is gener- 
ally nonlinear, as in Figs. 36, 37, 38, 39, 60, and 61. This varies 
from a more or less granular type (Fig. 42) to an oriented-alpha 
type (Figs. 36 and 37), with clearly defined beta grains. 

The iron was, with the exception of No. 209, found as fine 
globules often arranged in rows parallel to the axis of the rod. 

The Muntz metal and naval brass often showed in plain extruded 
form a nonlinear structure, illustrated in Figs. 48 and 69. In its 
extreme form this is shown in Fig. 96 of material No. 131, in 
which fracture was intercrystalline and characteristic of over- 
heated material. 

An interesting and rather unusual structure for commercial 
brasses is that of material No. 204, a naval brass, in which the 
so-called delta constituent ^^ is visible. This is shown in Figs. 
83 and 84 (light constituent). This constituent was very seldom 
found in the wrought brasses; it was apparently present also in 
No. 49, and possibly in No. 199. 

In three cases the practically pure beta structure was found, 
in Nos. 209-A, 209-B, and 211. (See Fig. 86 of material No. 
211.) 

2» S. If. Hoyt, Trans. Amer. Inst. Metals; 1915. 



Failure of Brass . 47 

An interesting type of structure (Fig. 87) is that of the threaded 
head of U-bolt 235, in which two generations of alpha are visible, 
the groundmass appearing much like a eutectoid. 

Considering those materials which failed because of inherent 
defects, such as the presence of. initial stresses or of incipient 
forging cracks, it can be stated that the structure alone does 
not indicate a latent tendency to crack or fail in this way. In 
particular, the presence of initial stresses is not indicated by the 
structure of these brasses. In alpha brass, on the other hand, 
the fact that a sample has received a large amount of cold work 
without a subsequent anneal, such that the initial stresses are 
high, may be detected by the presence of numerous "etch bands," 
as they have been called by Matthewson and Phillips ^^ The 
structure of a sample of such a brass which season cracked is shown 
in Fig. 85. 

One is accustomed, particularly in the case of pure metals, to 
associate a linear structure with initial stress, but the presence of 
such a structure in these brasses is, in fact, no criterion at all of 
the simultaneous presence of stresses, as may readily be seen by 
reference to the microstructure and data on initial stresses in 
the case of materials Nos. 83 and 161 . Material No. 83 has a linear 
structure and very low stresses, whereas No. 161, with an open 
nonlinear structure, possesses very high stresses, and combinations 
of this sort are quite common. 

Only one feature of structure has been found which is associated 
with failed and not with sound material, and that is the occurrence 
of large elongated beta grains, shown in Figs. 25 to 27. This 
structure has been found so far only in manganese-bronze lots 
which have failed, and seems to indicate a detail of manufacture, 
high temperatiire, or long period of heating above the diagram 
line bd, which is partially responsible at least for the presence of 
initial stress and tendency to season crack. Material having such 
a structure is certainly open to suspicion anyway, as one is inclined 
to associate large grain size and the oriented structure, which 
always goes with it, with brittleness, particularly to alternating 
stresses or impact. These materials having this structure do not, 
however, show brittleness in the tensile test, as will be seen by 
comparing the physical properties of materials Nos. 20, 158, 160, 
and 161, which possess this structure, to those of Nos. 136, 129, 
and 174, which possess a finer structure. 

'n C. H. Matthewson and A. Phillips, The Recrystallization of Alpha Brass on Annealing, Trans. Amer. 
Inst. Mining Engrs., 62, p. i; 1916. 



48 Technologic Papers of Ihe Bureau of Standards 

H. S. Primrose, in discussion,^' assigns as a reason for brittle- 
ness in a manganese bronze, as shown by an elongation of only 
8 per cent in 2 inches, the oriented structure of the material, 
which resembles that of material No. 158. As this latter material 
has, however, an elongation of 31 per cent, one can not evidently 
definitely relate brittleness with this structure. 

It may be remarked that there is some reas'>n to believe that 
he presence of the globules of iron in such materials renders them 
more sensitive to forging operations, and the presence of such 
particles may be assigned as a contributory factor in the failure 
of upset boltheads such as those of the Panama Canal. Bolt 
No. 247 was particularly rich in such particles. (See Fig. 88.) 

The variation in structure from edge to center was studied 
from the standpoint of obtaining an indication of the variation 
n work; done on the material from edge to center, which might 
be related to the value of the initial stresses. But in material 
No. 85, possessing very small stresses, there is a great variation 
in this structure (Figs. 47 and 48), whereas in No. 160 (Figs. 60 
and 61), possessing large stresses, the variation is insignificant. 

Unquestionably an indication could be obtained of the magni- 
tude of the initial stress through the structure if only one material 
were used and a definite and uniform method of manufacture 
were followed, but with so many variables in the situation it must 
be admitted that the structure can not be utilized directly for this 
purpose. 

3. SOME CORROSION AND ACCELERATION TEST 

The Heyn test with mercurous nitrate was carried out on several 
of the materials. This test is by many considered to give a fair 
criterion of whether a material will season crack, as it has been 
found that most brasses which season crack will crack within a 
short time in this solution. In these tests the brass specimens 
were immersed for four hours at ordinary temperature in a solution 
containing 65 gr. of HgNOs and 15 cc cone. HNO3 per liter. The 
specimens were of necessity short in most cases; that is, only 2 
inches long. 











Specimens 








3* 


40 


83 


103 


121 


140 


158* 


1164 


169* 


21 


54 


85 


109 


124 


142 


160* 


165 


a i-jo 


33 


57 


92 


116 


129 


153 


161 


166 


171* 


34 


67 


94 


118 


131 


156 


162 


167* 


a 172 


38 


75 


lOI 


120 


136* 


157 


163 


a 168 


173* 
"174 



« lo-incb specimens were also so tested, and gave the same behavior as the i-incb ones. 
^' Joum. Inst. Metal, 12, p. 53; 1914. 



Bureau of Standards Technologic Paper No. 82 




Fig. 13. — Alaterial No. i6g after immersion in -water for two weeks 



Failure of Brass 49 

Within this time (and afterwards) only the specimens marked 
with an asterisk, Nos. 3, 136, 158, 160, 167, 169, 171, and 173, 
cracked or showed any sign of fissure. Nos. 158 and 160 con- 
tained, after the test, transverse cracks only, No. 171 one longi- 
tudinal crack, and the others both. These cracks appeared 
generally in less than five minutes. From this it appears that only 
those materials crack under the mercurous-nitrate acceleration 
test which have at the surface tensional stresses above a certain 
value, which may provisionally be set at 30 000 pounds per square 
inch for the type of materials tested. Materials having compres- 
sion stresses at the surface, even when these are large (No. 164 had 
32 000 pounds per square inch compression at the surface), are not 
affected in this test. 

Furthermore, three specimens, Nos. 140, 142, and 118, having 
large tensional stresses at the surface, did not fail under this test. 
As these were typical of material which failed, one must conclude 
that this test is not a sufficient one ; material which fails under the 
test should not be accepted, but not all defective materials fail 
under this test. Results similar to the above were found with 
some few tests with ammonium hydroxide, which seems to act in 
the same way. 

It was desired to ascertain what action water alone would have 
on samples of these materials. A 6 or 8 inch sample of specimens 
136, 164, and 167 to 175 was immersed in a large water tank at the 
Bmeau on May 8 and allowed to remain for about four weeks. It 
may be recalled that material No. 167 is the same as 168, similarly 
169 and 170, 171 and 172, and 173 and 174, the only difference 
between the two samples of the same material in each of the four 
cases being that the samples with odd numbers, Nos. 167, 169, 171, 
and 173, were drawn very hard, whereas the others were given a 
comparatively light draw to size only, most of the work of forming 
having been done by extrusion. The stresses in the former group 
are large and the surface is in tension, whereas in the latter the 
stresses are small and the surface is in compression. No external 
stress was applied; nevertheless, during this time Nos. 169 and 171 
developed longitudinal cracks, and No. 167 both longitudinal and 
transverse ones. Fig. 13 shows the specimen 169. The other 
samples were not affected by this treatment (No. 173 was lost and 
no data is available on its behavior during this test) . 

These tests are interesting, first, as indicating what a slight 
impetus is necessary to cause failure in a material which is already 
59850—17 4 



50 Technologic Papers of the Bureau of Standards 

in a high initial stress, since the surface corrosion which took place 
in this time was insignificant. The specimens were merely tar- 
nished. During that time specimens of the same materials lying 
in the shop did not crack. 

4. HARDNESS VALUES 

The cause of the presence of initial stress is, as indicated above, 
to be sought either in the variation of the rate of cooling of different 
parts of the article, or in the differing degree to which different 
parts were deformed or worked, either hot or cold. It is to be 
expected that the properties of the material in the differently 
treated layers would be different, and Heyn^- has shown that this 
is true of the density, the elastic limit, and possibly also of the 
ultimate strength and elongation in the tensile test. The density, 
for instance, fs greater in the outer layer of a cold-drawn aluminum 
bronze bar than in the center ones. 

Determinations were made of the Brinell hardness of several 
samples of the brasses investigated in order to ascertain what 
relation, if any, existed between the amount of initial stress and 
the amount of variation of hardness from center to edge of these 
materials. Transversely cut specimens were taken and one 
impression made at the center and one or more at about 3 mm from 
the edge, and the hardness numeral calculated in each case. The 
results of these tests are given in Table 3. 

It is seen from the table that there is no reliable concordance 
between the hardness values or their variations and the values of 
the initial stresses. In general, the greater the initial stress the 
greater is the variation from edge to center of the hardness 
numeral, the latter being greater at the edge (except in one case, 
that of No. 205). But very definite exceptions to this relation 
are noted. The hardness variation for specimens of low initial 
stress is from i to 2 points, M^hereas that for several specimens 
of high initial stress is from 5 to 10 points. Yet No. 205, a speci- 
men of low stresses, is softer by about 8 points at the center than 
at the edge; No. 161 , of high stresses, has a difference of only about 
2 points in the value of the hardness numeral; and specimens 163 
and 186, of low initial stresses, have variations of from 8 to 9 
points in this value. Furthermore the Muntz metal 171-172, as 
finished hard, No. 171, shows no variation from center to edge of 
the hardness, whereas the same material. No. 172, finished softer, 
has a variation of 14 points. 

32 Loc. cit. 



Failure of Brass $t 

One is forced to conclude that there exists no possiblity of 
obtaining a reliable indication of the presence of initial stresses 
in a material through the study of the hardness numeral, nor 
consequently of the liability of such a material to season crack. 

5. DISCUSSION OF RESULTS 

In attempting to relate the occurrence of failures among lots 
of brass with the properties, etc., of the materials one is con- 
fronted by the fact of the simultaneous variation of two main 
factors — for example, the service stresses and the initial stresses. 
It is, however, possible to divide the materials which have been 
in service roughly into three classes, according to the severity of 
the service stresses. 

(i) Certain of the samples, comprising mostly drawn material, 
had season cracked in storage and before the application of any 
service stress whatever. These were Nos. i to 3, 7, 8, 9, 78, 
131, 160, 161, 167,^^ 169,^^ and 211. The fissures were trans- 
verse — that is, to axis of bar or rod — in Nos. 3, 7, -8, 9, 78, 160, 
and 161; longitudinal in No. 2, spiral in Nos. 167 and 169; and 
they took the form of square checker work inclined 45° to the 
axis of the bar in No. 211, as shown in Fig. 3. Reference to 
Table 5 shows that, where measured, these specimens, with the 
exception of No. 131, had tensional stresses in the outer layer 
varying from 26 000 to 83 000 pounds per square inch. In all 
cases in which the proportional limit of these materials was known 
the stress value in the outer layer was greater than the propor- 
tional limit. Furthermore, in each of these cases the average 
stress was high, representing a large amount of energy tending to 
rupture the bar. Failure in these cases was undoubtedly due 
primarily to the presence of initial stress, and these materials 
must be considered defective. 

In the case of No. 131 the outer layer was in severe compres- 
sion parallel to the cracks and to the flange bend and in tension 
at right angles to the cracks; this tension stress was low in value 
such that the initial stresses as measured can not be considered 
responsible for failure. The cracks occiured in the areas which 
had been bent by " heating a part of the plate in a forge and bend- 
ing it over a cast-iron form, then heating and bending another 
piece, and so on, until the whole circumference was flanged." 
This subsequent forging operation is in all probability responsible 
for failure in this case; it is probable that during the rapid and 

'2 These cracked while lying in the Bureau shops. 



52 Technologic Papers of the Bureau of Standards 

unequal cooling of the flanged part initial stresses were intro- 
duced which are not susceptible of measurement in the usual 
way. Such local stresses might be set up as a consequence of 
unequal coefficients of thermal expansion of the alpha and the 
beta constituents, and might readily be of a nature and magni- 
tude sufficient to start these cracks. 

(2) The second class comprises those articles, mostly bolts, 
which failed in service under moderate service stresses — that is, 
easily within the proportional limit of the material. These are 
Nos. 69 to 77, 107 to 117, 125, 126, 134, 137 to 139, 140 to 144, 
151, 152, 158, 159, 209, 235, and 247. Of these Nos. 107 to 117 
and 137 to 139 may have been subjected to service stresses as 
high as 1 5 000 pounds per square inch ; the others to stresses of 
lesser value. Nos. 69 to 77, 107 to 117, 140 to 144, 158 and 159 
possessed initial stresses of high average values ranging from 
9000 to 30 000 pounds per square inch. Nos. 74 and 116 showed 
compressional stress in the outer layer, whereas the others had 
in this layer high tensional stress. There is thus no diffi- 
culty in accounting for the cracking in the case of Nos. 140 to 
144, 158 and 159. The hook bolts, 107 to 117, all failed at the 
bend, and it is therefore probable that it was to a high initial 
bending stress that failure was due. The cracks always started 
from the concave side of the bend and Howard ^* has shown that 
this side of a brass bar bent cold is always in tension. These 
stresses unfortunately could not be measured. No. 74, represent- 
ing Nos. 69 to 77, presents the interesting case of a bolt which 
fractured in service under moderate load and in which there is a 
large initial compressive stress in the outer layers amounting to 
from ID 000 to 26 000 pounds per square inch. It is impossible 
to say whether failure started at the surface or not; no bolts 
have been found, however, showing cracks growing in from the 
surface, and it is therefore possible that fracture started at the 
center of the bolt (as in a transverse-fissured rail), where the 
initial tensional stress amounted to about 16 000 pounds per 
square inch. This would be contrary, it may be noted, to the 
fact generally obser\'ed that cracking of this type extends inward 
from the surface. 

The initial stresses in No. 125 could be measured only in a 
direction parallel to the fissures, and in this direction but mode- 
rate stresses were found. The authors believe that the stresses 
in a direction at right angles to this would be much more severe 
and in a reverse distribution ; that is, with tension at the surface. 

" Loc cit. 



Failure of Brass 53 

Thus it is believed that the presence of initial stresses was also 
in these cases a predominating factor in causing cracking, and these 
materials must also be looked upon as defective in the sense of 
possessing too high initial stresses. 

The other articles of this class had all received a subsequent 
heat treatment or forging operation, sometimes local in character; 
the cracks always appeared in those areas so treated, such that it 
is not to be expected that the initial stresses as measured often 
outside of these areas will bear any relation to the failure. This is 
in fact true. The stresses when measured were found to be low, 
and it is to a consideration of the operations performed on the 
material subsequent to the passing of the material out of the 
manufacturer's hands to which one must turn in quest of expla- 
nation of the failure. 

The bolts 137 to 139 were heated to about 600° C and quenched 
in water. The plate 209 had been flanged cold and afterwards 
annealed; the structure showed, however, that the two failed 
specimens, 209-B and 209-C, had been thereupon cooled very 
rapidly, perhaps quenched, whereas the sample which had not 
failed gave no structural indication of such severe treatment. 
Tests made by cooling samples of 209-C at different rates from 
about 750° C, and observing the structure showed that 209-A and 
209-B had been cooled more rapidly than can be done in a blast 
of cold air, presumably, therefore, quenched in water. 

Now one of the authors in connection with some other work 
had occasion to quench a i-inch diameter rod of an alloy, such as 
that of 209, from about 650° to 700° C in order to retain the pure 
beta structure. This was found literally cracked to pieces after 
such treatment, such that it could be almost crumbled in the 
hand. This indicates how sensitive such a material is to drastic 
treatment of this kind. 

Concerning No. 138, in which only slight stresses were meas- 
ured, it is believed that there may exist local stresses not suscept- 
ible of measurement in the usual way, set up during the rapid 
cooling of the heterogeneous alloy, due to a difference in the 
coefficient of expansion of the constituents alpha and beta. Some 
preliminary measurements of these coefficients made by D. H. 
Sweet and L. W. Schad, of this Bureau, would tend to bear out 
this view. 

The fracture in the manganese-bronze bolts, 235 and 247, from 
the Panama Canal, occurred within areas forged or upset, namely, 



54 Technologic Papers of the Bureau of Standards 

at a forge bend and in the upset threaded head of 235 and at the 
base of the liead (upset) in 247, and are undoubtedly caused by 
some improperly executed detail of this operation. Fracture 
occurred in both cases through cross sections of greater area than 
adjacent ones under the same total stress, but which had not been 
affected by the forging operation. 

One can assume that local and hence not readily determinable 
initial stresses were set up during forging, which were unrelieved 
and finally caused failure. But there is also another and very 
plausible explanation; that is, that invisible internal cracks were 
formed during forging, which opened up when a service stress was 
apphed. That such cracks are formed is a fact well known to 
manufacturers of manganese bronze, and it is also known that 
these materials have temperature zones in which they are quite 
brittle, and if work is done on them at these temperatures, the 
ductility is readily exhausted and cracks will appear. These may 
be so fine as to be almost invisible ; they often do not extend to the 
surface, but make known their presence only when a stress is 
applied which then opens them up. 

Bengough^^ says, concerning the ductility of his "complex" 
brass, which is somewhat similar to manganese bronze: "At high 
temperatures the ductility of bars of this alloy can not be satis- 
factorily measured, owing to the fact that numerous wide cracks 
opened up in the bar. * * * This phenomenon was also 
observed at all temperatures above 400° C, and at 700° C rendered 
elongation measurements useless." He found a diminution of 
ductility in this alloy in the neighborhood of 500° C. 

The fractured end of bolt 247 showed a second transverse crack 
about H inch back of the fracture. This material also contained 
perhaps the largest proportion of iron present as separate globules, 
undissolved, that the authors have yet seen. Large particles of 
such iron were also found during the machining of specimens, 
which totally ruined the tool. Such particles of iron would tend 
to promote the formation of such forging cracks. 

In these latter cases the fault can not be put upon the material, 
but more justly to the operation of forging, done perhaps by per- 
sons inexperienced in the handling of this material. As an illus- 
tration of this it is noted that the firm Q which carried out the 
flanging work on No. 131 are machinists and founders, manufac- 
turing sugar-refining machinery, and the rivets 10, 11, 132, "were 

•'* G. D. Bengough, A Study of the Properties of Alloys at High Temperatures, Journal of the Institute 
of Metals, 7, p. 123; 191?. 



Failure of Brass 55 

driven by an experienced boiler maker." There is no doubt of the 
danger of entrusting such work to men experienced only in steel 
working. 

(3) The third class comprises several lots of manganese-bronze 
bolts, used in making up flange joints, in which there is some doubt 
as to the magnitude of the service stress introduced by drawing the 
bolts up tight. The opinion is expressed by the engineers familiar 
with the work that all of the stud bolts 20 to 39, 40 to 48, and 189 
to 192, and many of the hexagon head bolts 49 to 68 and 193 to 
194, were draAvn up above the elastic limit of the material, an 
approximate estimate of 1 5 000 pounds per square inch having 
been assigned to this stress. Most unfortimately, from the stand- 
point of attempting to draw conclusions from the investigation of 
these bolts, this opinion is not borne out in the case at least of Nos. 
20 to 39 by a study of the initial stresses in the bolts which have 
failed. 

When such a bolt containing high initial stresses is stretched as a 
bolt above the elastic limit of the material, the value of the initial 
stresses must be diminished — the initial stress diagram flattened 
out; upon applying, for example, a tensional stress of 40 000 pounds 
per square inch (the value of the proportional limit) to the specimen 
1 64, the center portion will be under a stress of about 53 000 pounds 
per square inch and must yield, whereas the outer portions will be 
in tension varying from 30000 to 10 000 pounds per square inch 
and can not yield. Thus upon removing the applied stress the 
difference between the maximum tension and the maximum com- 
pression, taken algebraically, must be less by about 13 000 pounds 
than originally. This was actually done in the case of specimen 
164. After removal of the stress of 40 000 pounds per square inch 
the average stress had fallen from 1 2 000 pounds per square inch 
to about 5000 pounds per square inch. There is the possibility 
that in these thick, short bolts the bolting stress may itself have 
been very nonuniform, the load having been carried mostly at the 
periphery. In that case such a distribution of stresses as has been 
found in such bolts might have been preserved or even intensified 
upon drawing up above the elastic limit. 

Bolts, lot 20 to 39 and lot 189 to 192, were similar and had been 
subjected to the same service. Eighty-three per cent of the first 
lot failed, none of the second. The initial stresses were high, about 
1 5 000 pounds per square inch in average value in the first lot and 
low, about 7700 pounds per square inch, in the second. The 
fissures started from the surface at the base of the thread and ex- 



56 Technologic Papers of the Bureau of Standards 

tended inward, although the outer layers were in initial compres- 
sion, amounting at the base of the thread to 15 000 pounds per 
square inch in the case of No. 32. None of bolts 40 to 48 had failed, 
although about 16 per cent of the lot which they represent did. 
The average stresses are low, 4000 to 5000 pounds per square inch 
in these specimens. 

The only hexagon-head bolt, lot 49 to 68, which failed in the 
body of the bolt, not immediateh^ adjacent to the forged head, was 
No. 67, and in this case the outer layer was under an initial tension 
of 12 000 pounds per square inch. The other bolts of this lot 
showed low initial stresses and the fracture took place at the base 
of the thread or at the shoulder of the head. In the former cases 
one must assume that the service overstress was responsible lor 
failure, whereas in the latter, since the cross-sectional areas at the 
fracture were greater than at sections through the threaded portion 
of the bolt, one may conclude again that the forging of the heads 
was not correctly done. 

A great deal of material has been examined which has not 
failed, although it has nevertheless been in service under varying 
severe conditions. Such materials as have been indicated above 
do not differ markedly or consistently in their physical properties 
or structure from that which has failed. The initial stresses are, 
however, in general, found to be lower in magnitude than in the 
case of the latter. As instances of such material may be cited 
Nos. 41 and 43, 181 to 183, 184, 185 to 188, 189 to 192, 193 to 
200, 244, and 245. Of these, Nos. 184, 244, and 245 have been 
subjected to small service stresses; Nos. 181 to 183, 185 to 188, 
and 193 to 200 to moderate service stresses; and Nos. 40 to 48 
and 189 to 193 to severe service stresses. The average of the 
average initial stress in these samples is something less than 5000 
pounds per square inch. 

Furthermore, the experience on the Minneapolis filter plant 
with bolts and strainer plate, which have been thoroughly 
annealed, and thus relieved of initial stresses, is of the greatest 
value, since under the identical service conditions under which 20 
per cent of the similar, but unannealed, materials failed within 30 
days, after over one year, now absolutely no breakages have 
occurred. 

The next question that arises is that of the manner in which 
such failures as have been described may be prevented. It has 
been seen that there are several factors which may cause failure 



Failure of Brass 57 

of the general type in question, and for each of these factors a 
separate safeguard is needed. 

A number of failures have resulted from improper forging 
operations and heat treatment undertaken by persons not wholly 
familiar with the properties of the material. This has occurred 
mainly with manganese bronze (-^vith the exception of some naval 
brass plate, rivets, and bolts). There has resulted from the forg- 
ing of good material, in most cases, either a highly stressed con- 
dition within the forged area, or fine internal cracks have been 
formed which have afterwards opened up under stress. The 
obvious remedy for this is to intrust such operations only to men 
familiar with this material and its extreme sensitiveness to forg- 
ing operations at certain temperatvures. 

A number of failures have occurred in satisfactory material 
(bolts) as a result of overstressing in service. This opens up at 
once a large field for investigation into the question as to what 
are the safe working stresses for various 60:40 brasses and just 
how much they will stand abuse of the sort that does not appar- 
ently harm steel. This is a question, the answer to which must be 
reserved for future work to present; work has already been 
started along this line at this Bureau. Ernst Jonson *^ has 
already given a valuable contribution to the solution of this 
question in his work on the failure of brasses exposed to the 
action of concentrated ammonium hydroxide while under stress. 
He comes to the conclusion that any brass, irrespective of initial- 
stress distribution, will fail in this way when the stress value is 
kept for a few days or weeks at or just above the elastic (or pro- 
portional) limit, and his results, including tests made on an 
initial-stress free sample. No. 136, annealed, and on one with 
large compressional stress at the surface. No. 164, amply bear 
out his conslusion. He then carries this conclusion over to actual 
service conditions in which corrosion is by air and water instead 
of by ammonia, and states that again the true elastic limit is the 
highest stress which such a material will stand in tension, accom- 
panied by corrosion. The authors have in mind failures which 
have occurred in bmmed-in and other castings, which would lead 
them to agree with this conclusion also; but only a full investi- 
gation can definitely decide this point, and not until such investi- 
gation has been made can the designing engineer know definitely 
what he may expect of such materials. Until then it would seem 
that the history of materials such as 40 to 48, 181 to 200, 244 to 

"Loc. cit. 



58 Technologic Papers of the Bureau of Standards 

245, and that of the annealed bohs of the Minneapolis filtration 
plant would give assurance that, provided the material is free 
from initial stresses, these materials can be designed with entire 
safety to carry loads of about 5000 pounds per square inch, pos- 
sibly even 10 000 pounds per square inch, provided the true 
elastic limit is definitely above this value. 

Finally, a large percentage of the failures described were due 
wholly or in part to the presence of initial stress as measured. 
These stresses are introduced by those processes which give a 
brass article "work-hardness," and manufacturers claim that 
when one obtains such highly stressed material it is generally 
the result of an attempt on the buyer's part to set the physical 
specifications for tensile strength and yield point too high, with 
the result that the specification can only be met with initially 
highly stressed material. 

The question of safeguarding oneself against obtaining such 
defective material is a manifold one. One can most easily obtain 
stress-free material by specifying that it receive a sufficient final 
anneal (one hour at from 400° to 550° C) . By such treatment the 
initial stresses are almost wholly removed, and when a high value 
for the elastic limit is not required this is the only rational method 
to use. Indeed, if the annealing be done at not above 400° C, the 
material may still possess a high elastic Hmit as was shown in He. 
If this be not done, or in case assurance is wanted that it has been 
done, recourse must be taken to a direct measurement of the initial 
stresses as described above. The question then arises, what are 
the Umiting safe values for initial stresses ? To such a question no 
general reply can be given; the values of the initial stresses, which 
may be allowed in such materials, are dependent in any particular 
case upon external conditions and the physical properties of the 
materials. The authors are of the opinion (i) that it is dangerous 
to use any brass in which the tensional stress at the surface is 
nearly equal to the elastic limit; (2) that failure may occur when- 
ever the sum of the initial stress and the load stress in any layer is 
greater than the elastic limit of the material of that layer, particu- 
larly in the surface layer. Assuming then a case in which an 
average manganese bronze is used, with a proportional limit of from 
1 5 000 to 20 000 pounds per square inch and in which the service 
stresses, accompanied by moderate corrosion, amount to from 
5000 to 10 000 pounds per square inch, and bearing in mind that 
the average initial stress is the value most readily measured, one 
may conclude that an average initial stress value of 5000 pounds 



Failure of Brass 59 

per square inch is a safe one; with this value no layer would, except 
with unusual initial stress distribution, be subjected to a tensional 
stress above its proportional limit. 

This value probably errs on the safe side; it is probable that under 
certain circumstances higher stresses might be allowed without 
danger. It agrees, however, very well with those average values 
in materials, which have been in service and have not failed 
(under all but overload stresses), and may, it is believed, safely be 
accepted as a conservative upper average initial stress limit. 

This value also appears to agree well with the experience of 
manufacturers. The latter appear to have, generally speaking, a 
pretty definite knowledge of the upper limit of physical properties 
(ultimate strength and elastic limit) to which they may go with 
safety with their various materials, and beyond which the material 
is in danger of season cracking when exposed to corrosion. Now, 
in many cases, as indicated above, manufacturers were requested 
to furnish material possessing the greatest hardness which, in their 
opinion and experience, was still consistent with freedom from 
danger from season cracking. Samples which were sent in answer 
to this request, and which represent, as far as physical and other 
properties are concerned, what might be called the optimum 
manufacturing practice in these brasses, are Nos. 203 and 205." 

Materials Nos. 165, 166, 168, 170, 172, and 174 were sent in 
answer to a request for samples of material such as the manu- 
facturer would furnish for his highest specification contracts. 
This request involves, although less directly, the same idea, 
namely, that this material is supposed to be the hardest that the 
manufacturer recommends in consideration of the danger from 
cracking. It is now noted that, with two exceptions, Nos. 165 and 
166, both from- the same manufacturer, the values of the average 
initial stresses in these brasses are lower than 6000 pounds per 
square inch, and range approximately from 3000 to 6000 pounds 
per square inch. This concordance seems to be an independent 
corroboration of the authors' results, which is based upon the large 
experience of the producers of brass themselves, and gives this 
value a somewhat more general significance. 

" The manufacturer specifically stated in regard to these materials that in his opinion the latter possessed 
the highest ultimate strength and elastic limit in tension (for this type of material as manufactured by him) 
which were consistent with safety. 



6o 



Technologic Papers of the Bureau of Standards 
TABLE 8 



Correlation of Tensile Strength and Average Initial Stress in Manganese Bronze 

1 Inch Rods " 



B. S. No. 


Ultimate tensile 


Chemical analysis 






strength 


Copper 


Zinc 


Tin 


Iron 


Average initial siress 


173 


Ibs./in.2 

100 000 
84 000 
84 000 
79 000 
77 000 
72 000 
70 000 

61 000 

62 000 
72 000 


kg./cm.' 
7030 
5920 
5920 
5560 
5420 
5070 
4940 
4300 
4360 
5070 


Per cent 

57 
59 
57 
59 
57 
59 
60 
57 
57 
58 


Per cent 

40 
40 

40 
39 
41 
39 
39 
41 
41 
40 


Per cent 

1.6 
.4 

1.6 
9 

1.0 
.8 
.8 
.9 

1.0 
.7 


Per cent 

1.3 

1.0 

1.2 

1.0 

.6 

.7 

.5 

1.0 

1.5 

.7 


lbs./in.« 

37 000 

5000 

3000 

15 000 

6000 

22 000 

25 000 

30 000 

8000 

5000 


kg./cm,« 
2600 


205 


350 


174 


210 


129 


1050 


175 


420 


136 


1550 


3 


1760 


160 


2110 


189 


560 


6 


350 







o Round numbers are given here for the sake of convenience in comparing values. 
* This data it an average of a lot including Nos. 49, so, 54, 63, 67, and 68. 

TABLE 9 
Physical Properties and Initial Stresses in the Best Brasses Tested « 





Initial stress 


Physical properties in tension 




B.S.No. 


Average 


Maximum 


Ultimate 
strength 


Proportional 
limit 


Elon- 
gation 
in 2 
inches 


Re- 
duc- 
tion of 
area 


Kind of 
material 


174 

20s 

175 

85 

170 

203 

164 

172 


Ibs./in. 2 
3000 

5000 
6000 
1000 
7000 
5000 
12 000 
4000 


kg/cm' 
210 

350 
420 
70 
490 
350 
840 
230 


Ibs./in, 2 
9000 

9000 

9000 

2000 

12 000 

9000 

33 000 

11 000 


kg/cm2 
630 

630 
630 
140 
840 
630 
2320 
770 


Ibs./in. 2 

84 000 

85 000 
77 000 
61 000 
68 000 

71 000 

72 000 
64 000 


kg/cm2 
5910 

5980 
5420 
4290 
4800 
5000 
5060 
4500 


Ibs./in. 2 
36 000 

52 000 
26 000 
16 000 

43 000 

44 000 
40 000 
36 000 


kg/cm2 
2530 

3660 
1830 
1120 
3020 
3100 
2810 
2540 


P. ct. 

22 

22 
27 
47 
31 
31 
16 
40 


P.ct. 

20 

41 
27 
51 
47 
57 
50 
50 


Manganese 
bronze. 

Do. 

Do. 
Naval brass. 

Do. 

Do. 
Muntz metal. 

Do. 



o Values are given in round numbers. 

It was hoped that the tests made of these various materials, 
particularly those furnished directly by the manufacturers, would 
bring out some rough parallelism between initial stresses and 
hardness for a given material, such a relation as would give some 
indication as to what properties one might reasonably demand of 
such materials. This has not been true, however; no such rela- 
tion can be deduced, as is clearly shown from Table 8. All that 
can be done is to draw attention to certain examples as indicating 
what is possible. 



Failure of Brass 6i 

It is apparently possible to obtain commercially physical prop- 
erties, including hardness, in all of these materials sufficient to 
meet not only the New York Board of Water Supply specifica- 
tions, but many others given in the Appendix, page 63, and in 
conjunction with low values of the initial stress. An idea of what 
may be obtained in these materials can be had from Tables 8 and 9. 

One wonders, after consideration of specimens 205 and 175, 
with elastic Hmits of 52 000 and 76 000 pounds per square inch 
and average initial stresses of 5000 and 6000 pounds per square 
inch, respectively, why a specimen, such as 160 of the same mate- 
rial, with an elastic limit of only 14 000 pounds per square inch 
should have an average initial stress of 30 000 pounds per square 
inch. It is evident that the low values of the hardness and of 
the ultimate strength and elastic Umit in tension give no assur- 
ance that the material is not at the same time highly initially 
stressed. 

III. CONCLUSION 

1 . The results of the investigation have thus far shown that the 
failures occurring in the construction of the Catskill Aqueduct, in 
the Minneapolis Filtration Plant, and on the Panama Canal, in 
wrought-brass materials of the type 60:40, have been due (a) to 
the presence of initial stresses, either alone or in conjunction with 
external load ; (b) to faulty practice in forging bolt heads, flanging 
plate, etc. ; and (c) to overstress in service caused by drawing bolts 
up too tightly. These failures were thus partly due to defects in 
material, but must be ascribed in part to service abuse. 

2. These materials, speaking broadly, should, when sound and 
comparatively free from initial stresses, support service stresses of 
5000, or perhaps even up to 10 000 pounds per square inch without 
failing. If, however, there are present also initial stresses, there 
may be said to exist the possibility of cracking whenever the sum 
of the service tensional stress and the initial tensional stress in any 
layer, but particularly the outer layer exposed to corrosion, is 
greater than the proportional or elastic limit of the material in that 
layer. If, in the extreme case, the initial tensional stress in the 
outer layer is, itself, greater than the elastic limit, failure will take 
place before the application of any external stress; that is, the 
material will season crack. 

3. There is thus no definite value which may be assigned as a 
safe limit for initial stresses in such materials, for each case must 
be a law unto itself. However, assuming the average grade of mate- 
rial and the ordinary service stresses (tension) of about 5000 poimds 
per square inch, a value of 5000 pounds per square inch may be 



62 Technologic Papers of the Bureau of Standards 

assigned as a conservative limit for the allowable average initial 
stress; this refers particularly of course to rods. This value 
accords well (a) with such stress values found in materials which 
have given good service, and (6) with stress values found in rods 
fturnished by manufacturers as representing the hardest material 
which could be guaranteed against cracking. 

4. One-inch diameter rods of various 60:40 mixtures manu- 
factured to meet high physical specifications have contained 
average initial stresses averaging about 5000 to 6000 pounds per 
square inch. 

5. Too few samples have been investigated to allow of any 
definite conclusion as to how high specifications may be set for 
these materials, without undergoing danger that the product 
obtained may be too highly initially stressed. It seems, however, 
that it is possible to obtain ultimate strengths of 70 000 to 75 000 
pounds per square inch for a manganese bronze, those of 65 000 to 
70 000 pounds per square inch for naval brass, and from 60 000 to 
55 000 pounds per square inch in Mimtz metal, associated with 
initial stresses of sufficiently moderate value. Just how much higher 
one may go consistently is a question that can not yet be decided ; 
that these materials can, with .perhaps special treatment, be made 
with much higher ultimate strength is shown. It may be noted 
that the values given are not to be accepted necessarily as normal 
ones ; i. e. , to be specified by the engineer. In setting specifications 
the leeway necessary to the manufacturer must not be neglected. 

6. The surest convenient method of ascertaining the approxi- 
mate average value of the initial stresses in bars is by the Howard- 
Heyn elongation method, in which a strain gage may be used and 
heavy layers removed. 

The authors take this opportunity of expressing their apprecia- 
tion to the many who have aided iri this investigation. Dr. G. K. 
Burgess, at whose direction the work was carried out has been ever 
ready with helpful comment and suggestion. R. P. Devries and 
B. ly. Lasier have carried out the tensile and the Brinell hardness 
tests; A. B. Lort has made the chemical analyses. The materials 
and information concerning them have been furnished through the 
kindness of the New York Board of Water Supply, of the engineer's 
department of the city of Minneapolis, of the United States Navy 
Department, of the Panama Canal administration, and of many 
manufacturers. Helpful suggestions have been given by J. R. 
Freeman, A. D. Flinn, W. H. Bassett, E. Jonson, S. W. Miller, and 
many others. 

Washington, July 7, 1916. 



Appendix.— SPECIFICATIONS FOR WROUGHT BRASS 

1. U. S. NAVY SPECIFICATIONS 

(a) MANGANESE BRONZE (46B15. APR. 1, 1914) 

Manganese Bronze, Roi,led, or Composition Mn-r 

General Instructions 

1. General Instructions or Speciiications issued by the Bureau concerned shall form 
part of these specifications. 

Scrap 

2 . Scrap shall not be used in the manufacture, except such as may accumulate in the 
manufacturers' plant from material of the same composition of their own make. 

Chemical and Physical Requirements 

3. The chemical and physical requirements shall be as follows: 



Diameter 


Mini- 
mum 
tensile 
strength 


Mini- 
mum 
yield 
point 


Mini- 
mum 

ot 
elonga- 
tion 
in2 
inches 


Copper 


Tta 


Zinc 


Iron 


Lead 
(maxi- 
mum) 


Man- 
ganese 
(maxi- 
mum) 


1 incli and below... 
Above 1 inch 


lbs./in.2 
72 000 
70 000 


lbs. in.2 
36 000 
35 000 


Per cent 

1 30 


Per cent 

57-60 


Per cent 

0. 5-1. 5 


Per cent 

40-37 


Per cent 

0. 8-2. 


Per cent 

0.2 


Per cent 
0.3 



4. Thematerialmustnot contain more than O.I of i per cent of all elements in addi- 
tion to those allowed in the table above. 

Additional Tests 

5. Bars must stand: (a) Being hammered hot to a fine point; (b) being bent cold 
through an angle of 120° and to a radius equal to the diameter or thickness of the test 
bar. 

The bending test bar may be the full-size bar, or the standard bar of i inch width and 
one-half inch thickness. In the case of bending test pieces of rectangular section, the 
edges may be rounded ofE to a radius equal to one-fourth of the thickness. 
Surface Inspection 

6. Material must be free from cracks and all other injurious defects, clean, smooth, 
and must lie straight. All bars to be clean and straight, of uniform quaUty, size, and 
color. * * * 

Fractme 

8. The color of the fractiure section of test pieces and the grain of the material must 
be uniform throughout. 

Purposes For Which Used 

9. Rolled roimd rods requiring great strength where subject to corrosion and salt 
water — 

Valves stems, etc. 

Propeller blade bolts, air pump and condenser bolts, and parts requiring strength 
and incorrodibility. 

63 



64 



Technologic Papers of the Bureau of Standards 



(b) NAVAL BRASS (46B6b, MAY 1, 1915) 

R01.LBD Naval Brass, or Composition N-r, Bars, Shapes, Sheets, Plates, and 

Rods 
General Instructions 

1. General Specifications for the Inspection of Material, issued by the Navy Depart- 
ment, in effect at date of opening of bids, shall form part of these specifications. 

Scrap 

2. Scrap will not be used in the manufacture, except such as may accumulate in the 
manufacturers' plants from material of the same composition of their own make. 
Chemical and Physical Properties 

3. The chemical and physical requirements shall be as follows:' 



Copper 


Tin 


Zinc 


Iron, 


Lead, 

tnpTiTTII^fTl 


Per cent 

5»-63 


Per cent 

0. 15-1. 5 


Per cent 
Rem. 


Pel cent 

0.06 


Pel cent 
0.2 



Minimum 
tensile 
strength 


Minim iim 

yield 
point 


Minimum 
elongation 
in 2 inches 


lbs./in.» 


lt)s./in.> 


Per cent 


60 000 


27 000 


35 


58 000 


26 000 


40 


54 000 


25 000 


40 


60 000 


27 000 


30 


55 000 


28 000 


30 


54 000 


27 000 


35 


56 000 


26 000 


35 



Bend. 120° cold 



Rods (diameter): 

to J Inch 

Over i to 1 inch 

Over 1 inch 

Shapes: All 

Plates: 

to i inch up to 30 inches width . 

to J inch above 30 inches width 

Over i inch thick 



{Radius equals thick- 
ness. 

Do. 

Do. 
Do. 
Do. 



Test Pieces 

4. Test pieces for rounds and bars will be as nearly as possible of the same diameter 
as the rounds, or else they are not to be less than one-half inch diameter and taken at 
a distance from the circumference equal to one-half the radius of the rounds. 

Test pieces from plates and shapes will be of the 2-inch standard size specified as 
given in the "General Specifications for Inspection of Material. " 

Bending test bar may be the full-size bar or the standard bar of i inch width and 
yi inch thickness. In the case of bending test pieces of rectangular section the edges 
may be rounded off to a radius equal to one-fourth of the thickness. 

Surface Inspection 

5. Material must be free from all injurious defects, clean, straight, smooth, must 
lie flat, be of uniform color, quality, and size, and be within the gauge and weight 
tolerances. * * * 

Proprietary Materials 

8. Various composition materials, otherwise conforming to the specifications but 
manufactured under proprietary processes or having proprietary names, may be sub- 
mitted in bids for consideration of the bureau concerned. 

Tolerances 

9. No excess weight will be paid for and no single piece that weighs more than 5 
per cent above the calculated weight will be accepted. 



Failure of Brass 65 

Underweight and Gauge Tolerances (Width of Sheets or Plates) 



Tolerance. 



Under 48 
inches 



S per cent. 



48 to 60 
inches 



7 per cent. 



Over 60 
inches 



8 per cent. 



Plates and sheets shall not vary throughout their length or width more than the 
given tolerance. 

Fracture 

10. The color of the fracture section of test pieces and the grain of the material 
must be uniform throughout. 

Purposes For Which Used 

11. The material is suitable for the following purpose, especially if subject to corro- 
sion as by salt water: Bolts, studs, nutSj and turnbuckles; rolled rounds, used princi- 
pally for propeller blade bolts, air pump and condenser bolts and parts requiring 
strength and incorrodibility, and pump rods, tube sheets, supporting plates, and 
shafts for valves in water heads. 

2. NEW YORK BOARD OF WATER SUPPLY 

The following specifications were used just previous to the discovery of cracking in 
a large amount of the brasses: 

(o) The minimum physical properties of bronze shall, except as otherwise specified, 
be as follows: 

Castings: 

Ultimate tensile strength 65 000 pounds per square inch, 

Yield point 32 000 pounds per square inch, 

Elongation 25 per cent. 

Rolled material, thickness i inch and below: 

Ultimate strength 72 000 pounds per square inch, 

Yield point •. 36 000 pounds per square inch. 

Elongation. 28 per cent. 

Rolled material, thickness above i inch: 

Ultimate strength 70 000 pounds per square inch, 

Yield point 35 000 pounds per square inch. 

Elongation 28 per cent. 

After being forged into a bar, rolled or forged bronze shall stand first, hammering 
hot to a fine point; second, bending cold through an angle of 120° to a radius equal to 
the thickness of the bar. * * * 

Tensile strength of brass rivet rods shall be not less than 55 000 pounds per square 
inch. 

Yield point not less than 30 000 pounds per square inch. 

Elongation not less than 20 per cent. 

The following specifications were used after the discovery of cracking (1914): 

(6) Whenever the characteristics of any bronze or other material are not particularly 
specified, such approved material shall be used as is customary in iirst-class work of the 
nature for which the material is employed. 
59850—17 5 



66 Technologic Papers of the Bureau of Standards 

The minimum physical properties of bronze shall, except as otherwise specified, be 
as follows: 

Castings: 

Ultimate tensile strength 65 000 pounds per square inch. 

Yield point : 32 000 pounds per square inch, 

Elongation 25 per cent. 

Forgings: 

Ultimate tensile strength 70 000 poimds per square inch. 

Yield point 35 000 pounds per square inch. 

Elongation 28 per cent. 

Hot-rolled or extruded bronze : 

Ultimate tensile strength 68 000 pounds per square inch, ' 

Yield point 27 000 pounds per square inch. 

Elongation 30 per cent. 

Tensile strength of brass rivet rods shall be not less than 50 000 pounds per square 
inch. 

Yield point not less than 20 000 pounds per square inch. 

Elongation not less than 32 per cent. 

After being forged into a bar, rolled, forged or extruded bronze shall stand, first, 
hammering to a fine point; second, bending cold through an angle of 120° to a radius 
equal to the thickness of the bar, without showing signs of fracture. 

All forged, extruded, or rolled bronze shall be subjected to test with a scleroscope, 
and if hardness is found materially exceeding that typical of hot- worked metal, the 
bronze shall be rejected or annealed promptly, as directed. 

The present general specifications for brass (19 15) are as follows: 

Composition by Percentage 





Copper 


Tin 


lion 


Lead 


Zinc 




59-62 
59-62 
57-61 






0. 6 max. 
.2 max. 
.2 max. 




Naval brass . 




0.5-1.25 
. 5-1. 25 




Rem 




0. 5-2. 


Rem, 







Minimum Physical Requirements for Hot-Rolled, Extruded, and Annealed Material 





Yield 
point 


Ultimate 
strength 


Elonga- 
tion 




lbs./in.2 
20 000 
22 000 
27 000 


. lbs./in.2 
50 000 
56 000 
68 000 


Per cent 
32 




32 


Manganese bronze 


32 







Drawn Material Not Annealed 



Muntz metal 

Naval brass 

Manganese bronze 



25 000 


SO 000 


30 000 


60 000 


35 000 


70 000 



25 
25 
25 



For sheets and tubing the required minimum elongation shall be 5 per cent less than 
given in the table. All material shall stand being bent cold through an angle of 120° 
and to a radius equal to its diameter or thickness. Bars shall stand being hammered 



Failure of Brass 67 

hot to a fine point. Scrap shall not be used in the manufacture except such as comes 
from the same composition made in the same mill. The material shall be free from all 
injurious defects, and shall be clean, smooth, and straight and of uniform quality and 
size. Unless otherwise specially permitted, all bars shall be extruded or hot rolled 
and not subsequently drawn or cold rolled. The straightening of hot-worked material 
shall be done by simple bending, not accompanied by compression between two oppo- 
site rolls. Plates shall be hot rolled, except that sheets less than one-fourth inch 
may be cold rolled and annealed. All hot-rolled material shall be tested with the 
scleroscope, and if the hardness is found to exceed materially that typical of hot- 
worked metal the rods shall be annealed. 

Drawn and unannealed material shall be tested for initial strain . In case of material 
9ne-fotuth inch or more in thickness this test shall be made by measurement. When 
so tested the maximum strain shall not exceed 0.002 inch in a length of 4 inches. The 
-test specimen shall be ^H inches long. 

After the length has been measured the test specimen shall be cut down for a length 
of 4 inches, as follows: Bars shall be turned to one-third of the original diameter. 
Flats shall be machined to one-third the original width and thickness and plates and 
tubing to one-third the original thickness. The length shall then again be measured. 
The difference between the two measurements shall be regarded as the maximum 
initial strain. 

Bars shall be measured at three marked equidistant points on the circumference; 
flats and plates at two points, one at each edge. Test pieces of plates shall be 2 inches 
in width. Each measurement shall be the average of five observations at each meas- 
uring point. In testing tubing the entire section shall be used, one-third of the thick- 
ness being turned off on the outside and one-third bored out on the inside. Sheets and 
tubing less than one-foiurth inch in thickness shall be tested by immersion in a saturated 
solution of mercuric chloride for one hour, and then kept under observation for two 
weeks. If cracks appear during this test, the initial strain shall be regarded as exces- 
sive. When doubt exists the specimen shall be slightly bent to open cracks. Test 
pieces subjected to this test shall be 5^ inches long and 2 inches wide. 

3. SPECIFICATIONS OF THE ENGINEER'S DEPARTMENT OF THE CITY 
OF MINNEAPOLIS FOR BRASS BOLTS AND STRAINER PLATE 

specification no. 1 

Extracts prom Specifications for Strainer Plates for Repairs to Filters, 

City of Minneapolis, Minn. 



Sec. 3. Quality 

All strainer plates shall be made of Tobin bronze No. 14, Birmingham wire gage, 
having a tensile strength of at least 62 000 poimds per square inch and an elongation 
of not less than 25 per cent in 8 inches, with an elastic limit of at least one-half the ulti. 
mate tensile strength. When cold, the sheets must be capable of being bent 180° flat 
on themselves without fractiue on the outside of bent portion. All strainer holes shall 
be -^ inch in diameter and shall be drilled or punched before the plates are bent to 
the required shape. The plates shall butt at their ends and sides, and therefore must 
be smooth and true on all edges. All plates must be so made or cut as to give the 
greatest strength in a longitudinal direction. All hook bolts and ribs must be made 
of Tobin bronze, meeting the same requirements as to physical properties as above 
mentioned for the plates. The ^-inch round anchor rods may be made of a good 
quality of brass, phosphor bronze or Tobin bronze, the latter being preferred. 



68 Technologic Papers of the Bureau of Standards 

Sec. 4. Damaged Material 

Should any piece of the above material become damaged in any wa}^ either in han- 
dling or shipment in transit or before, it will be rejected and shall be removed from the 
work and another piece substituted immediately at the expense of the contractor. 

Sec. 5. Guarantee 

The contractor shall guarantee all material to be as specified and each piece of Tobin 
bronze must be marked "Tobin bronze" with the name of the firm manufacturing 
the same, the letters to be at least yi inch in height and plainly stamped in the metal. 
Failure to do this will be sufficient reasons for rejection. 

Sec. 6. Rejection 

An inspector, appointed by the city engineer, may, under instructions and direc- 
tions from the city engineer, inspect and supervise the work and material at the shop 
and see that the stipulations of the plans and specifications are faithfully performed. 
Tests shall be made under his personal supervision wherever he so requires, and the 
contractor shall furnish him with all the proper tools, specimens, appliances, and 
labor necessary. The passing of such inspection shall not release the contractor from 
his contract, and the material may be rejected at any subsequent period if found 
defective in any way. * * * 

SPECIFICATION NO. 2 

Extracts from Specifications for Strainer Pi<ates for New Fii^ters, MinnE- 

Apous, Minn., 1914 



Sec. 2. Workmanship and Materials 

The workmanship must be first class in all respects, and the materials the best of 
their respective kinds, and if at any time any piece of work is deemed by the city 
engineer or his lawful representative to be defective it shall be removed from the 
work immediately and be replaced by one acceptable to the city engineer. The cost 
of doing so must be borne by the contractor with no additional expense to the city. 

Sec. 3. Quality 

All strainer plates shall be made of Tobin bronze No. 14, Birmingham wire gage, 
having a tensile strength of at least 62 000 pounds per square inch and an elongation 
of not less than 25 per cent in 8 inches, with an elastic limit of at least one-half the 
ultimate tensile strength. When cold, the sheets must be capable of being bent 
180° flat on themselves witliout fracture on the outside of bent portion. All strainer 
holes shall be -^ Inch in diameter and shall be drilled or punched before the plates 
are bent to the required shape. The plates shall butt on their ends and sides, and 
therefore must be smooth and true on all edges. All plates must be so made or cut as 
to give the greatest strength in a longitudinal direction. All anchor bolts and ribs 
must be made of Tobin bronze, except as hereinafter provided. The anchor bolts 
must meet the same requirements as to physical properties as above mentioned for 
the plates. The ribs may be cast and when so made must be capable of withstand- 
ing a unit tensile stress of at least 42 000 pounds per square inch without fracture. 
The s^-inch round anchor rods may be made of a good quality of brass, phosphor 
bronze or Tobin bronze, the latter being preferred. All cast-iron base plates must 
be made from the best quality of gray pig iron, cough and even grained, and shall 
possess a tensile strength of at least 20 000 pounds per square inch. Specimen test 
bars of the cast iron used, each 26 inches long by 2 inches wide and i inch thick, shall 
be made without charge as often as the engineer may direct, and in default of definite 
instructions the contractor shall make and test at least one bar from each heat or nm 



Failure of Brass 69 

of metal. The bars when placed flatwise on supports 24 inches apart and loaded at 
the center shall support a load of 2200 pounds and show a deflection of not less than 
0.35 of an inch before breaking, or, if preferred, tensile, bars shall be made which 
will show a breaking point of not less than 20 000 pounds per square inch. Bars to 
be cast as nearly as possible to the dimensions without finishing, but corrections may 
be made by the engineer for variation in width and thickness, and the corrected result 
must conform to above requirements. 

Sec. 4. Defects in Castings 

Castings must be clean and perfect without blow or sand holes or defects of any 
kind. No plugging or other stopping of holes will be allowed. 

Sec. 5. Connecting Rods 

The contractor shall furnish all connection rods for the base plates as per plans 
accompanying these specifications. All connecting rods shall be made from the best 
quality of double-refined iron or steel and the threads are to be standard tap-bolt 
threads to fit the taps in the base-plate castings, one end being threaded left and the 
other right-hand thread. 

Sec. 6. Damaged Material 

Should any piece of the above material become damaged in any way either in 
handling or shipment in transit or before, it will be rejected and shall be removed 
rom the work and another piece substituted immediately at the expense of the 
contractor. 

Sec. 7. Guarantee 

The contractor shall guarantee all material to be as specified and each piece of Tobin 
bronze must be marked "Tobin bronze" with the name of the firm manufacturing 
the same, the letters to be at least }4 inch in height and plainly stamped in the metal. 
Failure to do this will be sufficient reasons for rejection. 

Sec. 8, Rejection 

An inspector, appointed by the city engineer, may, under instructions and direc- 
tions from the city engineer, inspect and supervise the work and material at the shop 
and see that the stipulations of the plans and specifications are faithfully performed. 
Tests shall be made under his personal supervision wherever he so requires, and the 
contractor shall furnish him with all the proper tools, specimens, appliances, and 
labor necessary. The passing of such inspection shall not release the contractor from 
his contract, and the material may be rejected at any subsequent period if found 
defective in any way. * * * 



PHOTOGRAPHS AND PHOTOMICROGRAPHS 

TABLE 10 
Photographs and Photomicrographs 



Fig. 
No. 



14.. 
15.. 
16.. 
17.. 
18.. 
19.. 
20.. 
21.. 
22.. 
23.. 
24.. 
25.. 
26.. 
27.. 
28.. 
29.. 
30.. 
31.. 
32.. 
33.. 
34.. 
35.. 
36. 
37. 
38. 
39. 
40. 
41. 
42. 
43. 
44. 
45. 
46. 
47. 
48. 
49. 
50. 
51. 
52. 
53. 
54. 
55. 



B. S. 

speci- 
men 



3 

11 

19 

28 

, 41 

50 

60 

94 

109 

134 

136 

158 

159 

161 

172 

185 

187 

189 

193 

195 

197 

204 

22 

22 

34 

34 

41 

41 

49 

67 

78 

83 

83 

85 

85 

116 

125 

129 

129 

136 

136 

140 



Mag- 
nified 



2 
2 
2 
2 
2 
2 

li 

2 

4 

2 

2 

2 

2 

2 

2 

2 

2 

1 

1 

2 

1 

2 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 



Etching 



Cu- 
Cu- 
Cu- 
Cu- 
Cu- 
Cu 
Cu. 
Cu- 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu- 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 
Cu 



Am-OH-2 
Am-OH-2 
■Am-OH-2. 
•Am-OH-2 
•Am-OH-2. 
-Am-OH-2. 
-Am-OH-2. 
-Am-OH-2. 
•Am-OH-2. 
-Am-OH-2. 
-Am-OH-2. 
•Am-OH-2. 
-Am-OH-2. 
-Am-OH-2. 
-Am-OH-2. 
■Am-OH-2. 
-Am-OH-2. 
■Am-OH-2. 
■Am-OH-2. 
■Am-OH-2. 
■Am-OH-2. 
■Am-OH-2. 
-Am-OH-1. 
-Am-OH-1. 
■Am-OH-1. 
-Am-OH-1. 
-Am-OH-1. 
-Am-OH-1 
-Am-OH-1 
-Am-OH-1 
-Am-OH-1 
Am-OH-1 
•Am-OH-1 
•Am-OH-1 
•Am-OH-1 
•Am-OH-1 
-Am-OH-1 
-Am-OH-1 
-Am-OH-1 
-Am-OH-1 
-Am-OH-1 
Am-OH-1 



Position 
of area 
plioto- 

graplied 



Edge. 

Center. 

Edge. 

Center. 

Edge. 

Center. 

Do. 

Do. 

Do. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 

Do. 



Fig. 

No. 



56.. 
57.. 
58.. 
59.. 
60.. 
61.. 
62.. 
63.. 
64.. 
65.. 
66.. 
67.. 
68-. 
69.. 
70.. 
71.. 
72.. 
73.. 
74-. 
75.. 
76.. 
77.. 
78., 
79., 
80-, 
81. 
82. 
83. 
84. 
85- 
86. 
87. 
88- 
89- 
90- 
91. 
92. 
93- 
94. 
95. 
96. 



B.S. 

speci- 
men 



156 

158 

159 

159 

160 

160 

161 

161 

166 

165 

167 

167 

168 

172 

175 

181 

181 

184 

184 

187 

187 

189 

189 

193 

195 

195 

197 

204 

204 

201A 

211 

235 

247 

31 

34 

38 

47 

78 
112 
138 
131 



Mag- 
nified 



50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
50 
25 
25 
25 
50 
50 
25 
50 
1000 
400 
25 
100 
100 
35 
20 
35 
20 
50 
20 
20 
20 



Etcliing 



Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH-: 
Cu-Am-OH. 
Cu-Am-OH 
Cu-Am-OH- 
Cu-Am-OH- 
Cu-Am-OH 
Cu-Am-OH-: 
Cu-Am-OH-: 
Cu-Am-OH- 
Cu-Am-OH. 
Cu-Am-OH. 
Cu-Am-OH. 
Cu-Am-OH. 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
Cu-Am-OH 
NH1OH+H2O2 
NH40H-fH202 
NaOH-fHjOs 
NH4OH-I-H2O2 
Cu-Am-OH-1. 
Cu-Am-OH-2- 
Cu-Am-OH-1 
Cu-Am-OH-1 
Cu-Am-OH-1 
Cu-Am-OH-1 
Cu-Am-OH-1 
Cu-Am-OH-1 



Position 
of area 
photo- 
graphed 



Center. 

Do. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 

Do. 

Do. 

Do. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 
Edge. 
Center. 

Do. 

Edge. 

Center. 

Do. 

Do. 



At fissure. 
Head. 
At fissure. 



71 



72 



Technologic Papers of the Bureau of Standards 
INITIAL STRESS DIAGRAMS 

TABLE 11 
List of Initial Stress Diagrams 



Fig. No. 


Material 


Remarks 


Fig. No. 


Material 


Remarks 


97 


3 


As received. 


109 


214-1 


As received, turned down. 


98 


32 


Do. 


110 


214-2 


As received, bored out. 


99 


43 


Do. 


Ill 


157 


Do. 


100 


67 


Do. 


112 


160 


As received. 


101 


74 


Do. 


113 


164 


Do. 


102 


92 


Do. 


114 


167 


Do. 


103 


136-2 


Do. 


115 


168 


Do. 


104 


136-24 


Do. 


116 


173 


Do. 


105 


136-50 


2J-lnch specimen. 


117 


174 


Do. 


106 


136-51 


10-incli specimen. 


118 


182 


Do. 


107 


136-a 


Bored out. 


119 


199 


Do. 


108 


136-6 


Annealed one hour at 400 ° C. 


120 


204 


Do. 



Note. — in all of the initial stress diagrams are plotted as abscissas, diameters squared in square 
inches, as ordinates initial fiber stresses in poimds per square inch. 



Bureau of Standards Technologic Paper No. 82 




Fig. 14 

Material 3 X 2 




Fig. is 

Material n X 2 




Fig. 16 

Material 19 X 2 



Fig. 17 
Material 28 X 2 



Bureau of Standards Technologic Paper No. 82 




Fig. i8 

Material 41 X 2 




Fig. 19 

Material 50 X 2 




Fig. 20 

Material 60 X i-s 







Fig. 21 
Material 94 X 2 



Bureau of Standards Technologic Paper No. 82 




Fig. 22 

Material 109 X 4 




Fig. 23 

JIaterial 134 X 2 




Fig. 24 
Material 136 X 2 



Fig. 25 

Material 158 X 2 



Bureau of Standards Technologic Paper No. 82 




Fig. 26 

Material 159 X 2 




Fig. 27 
Material 161 X 2 




Fig. 28 

Material 172 X 2 




Fig. 29 

Material 185 X 2 



Bureau of Standards Technologic Paper No. 82 




Fig. 30 
Material 1S7 X 2 







Fig. 31 

Material 189 X i 




Fig. 32 

Material 193 X i 



Fig. ss 

Material 195 X 2 



Bureau of Standards Technologic Paper No. 82 




Fig. 34 

Material 197 X 1 




Fig. 3s 

Material 204 X 2 



Bureau of Standards Technologic Paper No. 82 





Fig. 36 

Material 22 (edge) X so 



Fig. 37 

Material 22 (center) X 50 








Fig. 38 

Material 34 (edge) X so 



Fig. 39 

Material 34 (center) X so 



Bureau of Standards Technologic Paper No. 82 





Fig. 40 

Material 41 (edge) X so 



Fig. 41 

Material 41 (center) X 50 





Fig. 42 
Material 49 (center) X 50 



Fig. 43 
Material 67 (center) X 50 



Bureau of Standards Technologic Paper No. 82 




Fig. 44 

Material 78 (center) X 50 




Fig. 45 
Material 83 (edge) X so 





Fig. 46 

Material 83 (center) X 50 



Fig. 47 

Material 85 (edge) X 50 



Bureau of Standards Technologic Paper No. 82 





Fig. 48 

Material 85 (center) X 50 



Fig. 49 

Material 116 (edge) X 50 





Fig. 50 
Material 125 (center) X so 



Fig. 51 
Material 129 (edge) X 50 



Bureau of Standards Technologic Paper No. 82 




Fig. 52 

Material 129 (center) X 50 




Fig- 53 

Material 136 (edge) X so 





Fig. 54 

Material 136 (center) X 50 



Fig. 55 

Material 140 (center) X 5° 



Bureau of Standards Technologic Paper No. 82 




Fig. 56 

Material 156 (center) X 50 




Fig. 57 

Material 158 (center) X 50 




Fig. 58 

Material 159 (edge) X so 



Fig. 59 
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